diff --git a/app/contracts/reminders/base_contract.rb b/app/contracts/reminders/base_contract.rb
new file mode 100644
index 000000000000..b539f96f6361
--- /dev/null
+++ b/app/contracts/reminders/base_contract.rb
@@ -0,0 +1,82 @@
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) 2012-2024 the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+module Reminders
+  class BaseContract < ::ModelContract
+    MAX_NOTE_CHARS_LENGTH = 80
+
+    attribute :creator_id
+    attribute :remindable_id
+    attribute :remindable_type
+    attribute :remind_at
+    attribute :note
+
+    validate :validate_creator_exists
+    validate :validate_acting_user
+    validate :validate_remindable_exists
+    validate :validate_manage_reminders_permissions
+    validate :validate_remind_at_is_in_future
+    validate :validate_note_length
+
+    def self.model = Reminder
+
+    private
+
+    def validate_creator_exists
+      errors.add :creator, :not_found unless User.exists?(model.creator_id)
+    end
+
+    def validate_acting_user
+      errors.add :creator, :invalid unless model.creator_id == user.id
+    end
+
+    def validate_remindable_exists
+      errors.add :remindable, :not_found if model.remindable.blank?
+    end
+
+    def validate_remind_at_is_in_future
+      if model.remind_at.present? && model.remind_at < Time.current
+        errors.add :remind_at, :datetime_must_be_in_future
+      end
+    end
+
+    def validate_note_length
+      if model.note.present? && model.note.length > MAX_NOTE_CHARS_LENGTH
+        errors.add :note, :too_long, count: MAX_NOTE_CHARS_LENGTH
+      end
+    end
+
+    def validate_manage_reminders_permissions
+      return if errors.added?(:remindable, :not_found)
+
+      unless user.allowed_in_project?(:manage_own_reminders, model.remindable.project)
+        errors.add :base, :error_unauthorized
+      end
+    end
+  end
+end
diff --git a/app/contracts/reminders/create_contract.rb b/app/contracts/reminders/create_contract.rb
new file mode 100644
index 000000000000..6bc3c01eb76a
--- /dev/null
+++ b/app/contracts/reminders/create_contract.rb
@@ -0,0 +1,32 @@
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) 2012-2024 the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+module Reminders
+  class CreateContract < BaseContract
+  end
+end
diff --git a/app/contracts/reminders/delete_contract.rb b/app/contracts/reminders/delete_contract.rb
new file mode 100644
index 000000000000..06895868e6c4
--- /dev/null
+++ b/app/contracts/reminders/delete_contract.rb
@@ -0,0 +1,36 @@
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) 2012-2024 the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+module Reminders
+  class DeleteContract < ::DeleteContract
+    delete_permission -> {
+      # The user can delete the reminder if they created it
+      model.creator_id == user.id
+    }
+  end
+end
diff --git a/app/contracts/reminders/update_contract.rb b/app/contracts/reminders/update_contract.rb
new file mode 100644
index 000000000000..de462cfec17d
--- /dev/null
+++ b/app/contracts/reminders/update_contract.rb
@@ -0,0 +1,41 @@
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) 2012-2024 the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+module Reminders
+  class UpdateContract < BaseContract
+    validate :unchangeable_attributes
+
+    private
+
+    def unchangeable_attributes
+      if model.remindable_changed? || model.creator_id_changed?
+        errors.add(:base, :unchangeable)
+      end
+    end
+  end
+end
diff --git a/app/models/concerns/remindable.rb b/app/models/concerns/remindable.rb
new file mode 100644
index 000000000000..d55e65bf912b
--- /dev/null
+++ b/app/models/concerns/remindable.rb
@@ -0,0 +1,35 @@
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) 2012-2024 the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+module Remindable
+  extend ActiveSupport::Concern
+
+  included do
+    has_many :reminders, as: :remindable, dependent: :destroy
+  end
+end
diff --git a/app/models/notification.rb b/app/models/notification.rb
index 65dff4c23ab5..e21493cc10db 100644
--- a/app/models/notification.rb
+++ b/app/models/notification.rb
@@ -40,17 +40,20 @@ class Notification < ApplicationRecord
     responsible: 9,
     date_alert_start_date: 10,
     date_alert_due_date: 11,
-    shared: 12
+    shared: 12,
+    reminder: 13
   }.freeze
 
-  enum reason: REASONS,
-       _prefix: true
+  enum :reason, REASONS, prefix: true
 
   belongs_to :recipient, class_name: "User"
   belongs_to :actor, class_name: "User"
   belongs_to :journal
   belongs_to :resource, polymorphic: true
 
+  has_one :reminder_notification, dependent: :destroy
+  has_one :reminder, through: :reminder_notification
+
   include Scopes::Scoped
   scopes :unsent_reminders_before,
          :mail_reminder_unsent,
diff --git a/app/models/reminder.rb b/app/models/reminder.rb
new file mode 100644
index 000000000000..1228420fc19d
--- /dev/null
+++ b/app/models/reminder.rb
@@ -0,0 +1,51 @@
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) 2012-2024 the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+class Reminder < ApplicationRecord
+  belongs_to :remindable, polymorphic: true
+  belongs_to :creator, class_name: "User"
+
+  has_many :reminder_notifications, dependent: :destroy
+  has_many :notifications, through: :reminder_notifications
+
+  def unread_notifications?
+    unread_notifications.exists?
+  end
+
+  def unread_notifications
+    notifications.where(read_ian: [false, nil])
+  end
+
+  def completed?
+    completed_at.present?
+  end
+
+  def scheduled?
+    job_id.present? && !completed?
+  end
+end
diff --git a/app/models/reminder_notification.rb b/app/models/reminder_notification.rb
new file mode 100644
index 000000000000..cbdd70905a9b
--- /dev/null
+++ b/app/models/reminder_notification.rb
@@ -0,0 +1,4 @@
+class ReminderNotification < ApplicationRecord
+  belongs_to :reminder
+  belongs_to :notification
+end
diff --git a/app/models/work_package.rb b/app/models/work_package.rb
index a1ec03892668..a16611e48b03 100644
--- a/app/models/work_package.rb
+++ b/app/models/work_package.rb
@@ -41,6 +41,7 @@ class WorkPackage < ApplicationRecord
   include WorkPackages::Relations
   include ::Scopes::Scoped
   include HasMembers
+  include Remindable
 
   include OpenProject::Journal::AttachmentHelper
 
diff --git a/app/services/concerns/reminders/service_helpers.rb b/app/services/concerns/reminders/service_helpers.rb
new file mode 100644
index 000000000000..b6e27e2d446a
--- /dev/null
+++ b/app/services/concerns/reminders/service_helpers.rb
@@ -0,0 +1,57 @@
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+module Reminders
+  module ServiceHelpers
+    extend ActiveSupport::Concern
+
+    def reschedule_reminder(reminder)
+      destroy_scheduled_reminder_job(reminder)
+      mark_unread_notifications_as_read_for(reminder)
+      schedule_new_reminder_job(reminder)
+    end
+
+    def schedule_new_reminder_job(reminder)
+      job = Reminders::ScheduleReminderJob.schedule(reminder)
+      reminder.update_columns(job_id: job.job_id)
+    end
+
+    def destroy_scheduled_reminder_job(reminder)
+      return unless reminder.scheduled?
+      return unless job = GoodJob::Job.find_by(id: reminder.job_id)
+
+      job.destroy unless job.finished?
+    end
+
+    def mark_unread_notifications_as_read_for(reminder)
+      return unless reminder.unread_notifications?
+
+      reminder.unread_notifications.update_all(read_ian: true, updated_at: Time.zone.now)
+    end
+  end
+end
diff --git a/app/services/reminders/create_service.rb b/app/services/reminders/create_service.rb
new file mode 100644
index 000000000000..340f980a289f
--- /dev/null
+++ b/app/services/reminders/create_service.rb
@@ -0,0 +1,39 @@
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) 2012-2024 the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+module Reminders
+  class CreateService < ::BaseServices::Create
+    include Reminders::ServiceHelpers
+
+    def after_perform(service_call)
+      schedule_new_reminder_job(service_call.result)
+
+      service_call
+    end
+  end
+end
diff --git a/app/services/reminders/delete_service.rb b/app/services/reminders/delete_service.rb
new file mode 100644
index 000000000000..8250ffe12f8f
--- /dev/null
+++ b/app/services/reminders/delete_service.rb
@@ -0,0 +1,39 @@
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) 2012-2024 the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+module Reminders
+  class DeleteService < ::BaseServices::Delete
+    include Reminders::ServiceHelpers
+
+    def destroy(reminder)
+      destroy_scheduled_reminder_job(reminder)
+      mark_unread_notifications_as_read_for(reminder)
+      reminder.update(completed_at: Time.zone.now)
+    end
+  end
+end
diff --git a/app/services/reminders/set_attributes_service.rb b/app/services/reminders/set_attributes_service.rb
new file mode 100644
index 000000000000..c1cbff56aa64
--- /dev/null
+++ b/app/services/reminders/set_attributes_service.rb
@@ -0,0 +1,32 @@
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) 2012-2024 the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+module Reminders
+  class SetAttributesService < ::BaseServices::SetAttributes
+  end
+end
diff --git a/app/services/reminders/update_service.rb b/app/services/reminders/update_service.rb
new file mode 100644
index 000000000000..9a1bd002e1cd
--- /dev/null
+++ b/app/services/reminders/update_service.rb
@@ -0,0 +1,47 @@
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) 2012-2024 the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+module Reminders
+  class UpdateService < ::BaseServices::Update
+    include Reminders::ServiceHelpers
+
+    def after_perform(service_call)
+      reschedule_reminder(service_call.result) if remind_at_changed?
+
+      service_call
+    end
+
+    private
+
+    def remind_at_changed?
+      # For some reason reminder.remind_at_changed? returns false
+      # so we assume a change if remind_at is present in the params (would have passed contract validation)
+      params[:remind_at].present?
+    end
+  end
+end
diff --git a/app/workers/reminders/schedule_reminder_job.rb b/app/workers/reminders/schedule_reminder_job.rb
new file mode 100644
index 000000000000..522dad565bc0
--- /dev/null
+++ b/app/workers/reminders/schedule_reminder_job.rb
@@ -0,0 +1,65 @@
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+module Reminders
+  class ScheduleReminderJob < ApplicationJob
+    queue_with_priority :notification
+
+    def self.schedule(reminder)
+      set(wait_until: reminder.remind_at).perform_later(reminder)
+    end
+
+    def perform(reminder)
+      return if reminder.unread_notifications?
+
+      create_notification_service = create_notification_from_reminder(reminder)
+
+      create_notification_service.on_success do |service_result|
+        ReminderNotification.create!(reminder:, notification: service_result.result)
+      end
+
+      create_notification_service.on_failure do |service_result|
+        Rails.logger.error do
+          "Failed to create notification for reminder #{reminder.id}: #{service_result.message}"
+        end
+      end
+    end
+
+    private
+
+    def create_notification_from_reminder(reminder)
+      Notifications::CreateService
+        .new(user: reminder.creator)
+        .call(
+          recipient_id: reminder.creator_id,
+          resource: reminder.remindable,
+          reason: :reminder
+        )
+    end
+  end
+end
diff --git a/config/initializers/permissions.rb b/config/initializers/permissions.rb
index 87f571f46a9d..cfb6f057f713 100644
--- a/config/initializers/permissions.rb
+++ b/config/initializers/permissions.rb
@@ -212,6 +212,11 @@
                      {},
                      permissible_on: :project_query,
                      require: :loggedin
+
+      map.permission :manage_own_reminders,
+                     {},
+                     permissible_on: :project,
+                     require: :member
     end
 
     map.project_module :work_package_tracking, order: 90 do |wpt|
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 8535ce37aef1..4f88191d792c 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -1071,6 +1071,7 @@ en:
         not_an_integer: "is not an integer."
         not_an_iso_date: "is not a valid date. Required format: YYYY-MM-DD."
         not_same_project: "doesn't belong to the same project."
+        datetime_must_be_in_future: "must be in the future."
         odd: "must be odd."
         regex_match_failed: "does not match the regular expression %{expression}."
         regex_invalid: "could not be validated with the associated regular expression."
@@ -3214,6 +3215,7 @@ en:
   permission_select_project_modules: "Select project modules"
   permission_share_work_packages: "Share work packages"
   permission_manage_types: "Select types"
+  permission_manage_own_reminders: "Create own reminders"
   permission_view_project: "View projects"
   permission_view_changesets: "View repository revisions in OpenProject"
   permission_view_commit_author_statistics: "View commit author statistics"
diff --git a/config/locales/js-en.yml b/config/locales/js-en.yml
index 761b7a5153c6..9ed3ae60a345 100644
--- a/config/locales/js-en.yml
+++ b/config/locales/js-en.yml
@@ -676,6 +676,7 @@ en:
         prioritized: "Prioritized"
         dateAlert: "Date alert"
         shared: "Shared"
+        reminder: "Reminder"
       date_alerts:
         milestone_date: "Milestone date"
         overdue: "Overdue"
diff --git a/db/migrate/20241119131205_create_reminders.rb b/db/migrate/20241119131205_create_reminders.rb
new file mode 100644
index 000000000000..1ad0989de80a
--- /dev/null
+++ b/db/migrate/20241119131205_create_reminders.rb
@@ -0,0 +1,42 @@
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+class CreateReminders < ActiveRecord::Migration[7.1]
+  def change
+    create_table :reminders do |t|
+      t.references :remindable, polymorphic: true, null: false
+      t.references :creator, null: false, foreign_key: { to_table: :users }
+      t.datetime :remind_at, null: false
+      t.datetime :completed_at
+      t.string :job_id
+      t.text :note
+
+      t.timestamps
+    end
+  end
+end
diff --git a/db/migrate/20241121113638_create_reminder_notifications.rb b/db/migrate/20241121113638_create_reminder_notifications.rb
new file mode 100644
index 000000000000..0e92b9dab99e
--- /dev/null
+++ b/db/migrate/20241121113638_create_reminder_notifications.rb
@@ -0,0 +1,42 @@
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+class CreateReminderNotifications < ActiveRecord::Migration[7.1]
+  def change
+    create_table :reminder_notifications do |t|
+      t.references :reminder, foreign_key: true
+      t.references :notification, foreign_key: true
+
+      t.timestamps
+    end
+
+    add_index :reminder_notifications, :notification_id,
+              unique: true,
+              name: "index_reminder_notifications_unique"
+  end
+end
diff --git a/db/migrate/20241129135602_populate_manage_own_reminders_permission.rb b/db/migrate/20241129135602_populate_manage_own_reminders_permission.rb
new file mode 100644
index 000000000000..586be7102374
--- /dev/null
+++ b/db/migrate/20241129135602_populate_manage_own_reminders_permission.rb
@@ -0,0 +1,40 @@
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+require Rails.root.join("db/migrate/migration_utils/permission_adder")
+
+class PopulateManageOwnRemindersPermission < ActiveRecord::Migration[7.1]
+  def up
+    ::Migration::MigrationUtils::PermissionAdder
+      .add(:view_project,
+           :manage_own_reminders)
+  end
+
+  # No-op
+  def down; end
+end
diff --git a/frontend/src/app/features/in-app-notifications/center/in-app-notification-center.component.ts b/frontend/src/app/features/in-app-notifications/center/in-app-notification-center.component.ts
index 641983075d1f..70b4f0c8eea2 100644
--- a/frontend/src/app/features/in-app-notifications/center/in-app-notification-center.component.ts
+++ b/frontend/src/app/features/in-app-notifications/center/in-app-notification-center.component.ts
@@ -101,6 +101,10 @@ export class InAppNotificationCenterComponent implements OnInit {
       key: 'shared',
       title: this.I18n.t('js.notifications.reasons.shared'),
     },
+    {
+      key: 'reminder',
+      title: this.I18n.t('js.notifications.reasons.reminder'),
+    },
   ];
 
   selectedFilter = this.reasonMenuItems.find((item) => item.key === this.urlParams.get('name'))?.title;
diff --git a/lib/api/v3/notifications/property_factory.rb b/lib/api/v3/notifications/property_factory.rb
index f5786d253ef3..5b450656df9b 100644
--- a/lib/api/v3/notifications/property_factory.rb
+++ b/lib/api/v3/notifications/property_factory.rb
@@ -88,12 +88,7 @@ def concrete_factory_for(notification)
       end
 
       @concrete_factory_for ||= Hash.new do |h, property_key|
-        h[property_key] = if property_key == "shared"
-                            # for some reasons
-                            # API::V3::Notifications::PropertyFactory.const_defined?(property_key.camelcase)
-                            # returns true for shared only to fail on the constantize later on.
-                            API::V3::Notifications::PropertyFactory::Default
-                          elsif API::V3::Notifications::PropertyFactory.const_defined?(property_key.camelcase)
+        h[property_key] = if API::V3::Notifications::PropertyFactory.const_defined?(property_key.camelcase, false)
                             "API::V3::Notifications::PropertyFactory::#{property_key.camelcase}".constantize
                           else
                             API::V3::Notifications::PropertyFactory::Default
diff --git a/spec/contracts/reminders/base_contract_spec.rb b/spec/contracts/reminders/base_contract_spec.rb
new file mode 100644
index 000000000000..1dc9fcd654d4
--- /dev/null
+++ b/spec/contracts/reminders/base_contract_spec.rb
@@ -0,0 +1,137 @@
+# frozen_string_literal: true
+
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+require "spec_helper"
+require "contracts/shared/model_contract_shared_context"
+
+RSpec.describe Reminders::BaseContract do
+  include_context "ModelContract shared context"
+
+  let(:contract) { described_class.new(reminder, user) }
+  let(:user) { build_stubbed(:admin) }
+  let(:creator) { user }
+  let(:reminder) { build_stubbed(:reminder, creator:) }
+
+  before do
+    User.current = user
+    allow(User).to receive(:exists?).with(user.id).and_return(true)
+  end
+
+  describe "admin user" do
+    it_behaves_like "contract is valid"
+  end
+
+  describe "non-admin user" do
+    context "with valid permissions" do
+      let(:user) { build_stubbed(:user) }
+
+      before do
+        mock_permissions_for(user) do |mock|
+          mock.allow_in_project(:manage_own_reminders, project: reminder.remindable.project)
+        end
+      end
+
+      it_behaves_like "contract is valid"
+    end
+
+    context "without valid permissions" do
+      let(:user) { build_stubbed(:user) }
+
+      it_behaves_like "contract is invalid", base: :error_unauthorized
+    end
+  end
+
+  describe "validate creator exists" do
+    context "when creator does not exist" do
+      before { allow(User).to receive(:exists?).with(user.id).and_return(false) }
+
+      it_behaves_like "contract is invalid", creator: :not_found
+    end
+  end
+
+  describe "validate acting user" do
+    context "when the current user is different from the remindable acting user" do
+      let(:different_user) { build_stubbed(:user) }
+
+      before do
+        allow(User).to receive(:exists?).with(different_user.id).and_return(true)
+        reminder.creator = different_user
+      end
+
+      it_behaves_like "contract is invalid", creator: :invalid
+    end
+  end
+
+  describe "validate remindable object" do
+    context "when remindable is blank" do
+      before { reminder.remindable = nil }
+
+      it_behaves_like "contract is invalid", remindable: :not_found
+    end
+
+    context "when remindable is a work package" do
+      let(:work_package) { build_stubbed(:work_package) }
+
+      before { reminder.remindable = work_package }
+
+      it_behaves_like "contract is valid"
+    end
+  end
+
+  describe "validate remind at is in future" do
+    context "when remind at is in the past" do
+      before { reminder.remind_at = 1.day.ago }
+
+      it_behaves_like "contract is invalid", remind_at: :datetime_must_be_in_future
+    end
+
+    context "when remind at is in the future" do
+      before { reminder.remind_at = 1.day.from_now }
+
+      it_behaves_like "contract is valid"
+    end
+  end
+
+  describe "validate note length" do
+    context "when note is too long" do
+      before { reminder.note = "a" * (described_class::MAX_NOTE_CHARS_LENGTH + 1) }
+
+      it_behaves_like "contract is invalid", note: :too_long
+    end
+
+    context "when note is within the limit" do
+      before { reminder.note = "a" * described_class::MAX_NOTE_CHARS_LENGTH }
+
+      it_behaves_like "contract is valid"
+    end
+  end
+
+  include_examples "contract reuses the model errors"
+end
diff --git a/spec/contracts/reminders/delete_contract_spec.rb b/spec/contracts/reminders/delete_contract_spec.rb
new file mode 100644
index 000000000000..2d884059023b
--- /dev/null
+++ b/spec/contracts/reminders/delete_contract_spec.rb
@@ -0,0 +1,48 @@
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+require "spec_helper"
+require "contracts/shared/model_contract_shared_context"
+
+RSpec.describe Reminders::DeleteContract do
+  include_context "ModelContract shared context"
+
+  let(:contract) { described_class.new(reminder, current_user) }
+  let(:current_user) { build_stubbed(:admin) }
+  let(:reminder) { build_stubbed(:reminder, creator: current_user) }
+
+  context "when user is different from the one that created the reminder" do
+    let(:another_user) { build_stubbed(:admin) }
+
+    before { reminder.creator = another_user }
+
+    it_behaves_like "contract user is unauthorized"
+  end
+
+  include_examples "contract reuses the model errors"
+end
diff --git a/spec/contracts/reminders/update_contract_spec.rb b/spec/contracts/reminders/update_contract_spec.rb
new file mode 100644
index 000000000000..3f58ed19b0d2
--- /dev/null
+++ b/spec/contracts/reminders/update_contract_spec.rb
@@ -0,0 +1,68 @@
+# frozen_string_literal: true
+
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+require "spec_helper"
+require "contracts/shared/model_contract_shared_context"
+
+RSpec.describe Reminders::UpdateContract do
+  include_context "ModelContract shared context"
+
+  let(:contract) { described_class.new(reminder, user) }
+  let(:user) { build_stubbed(:admin) }
+  let(:creator) { user }
+  let(:reminder) { build_stubbed(:reminder, creator:) }
+
+  before do
+    User.current = user
+    allow(User).to receive(:exists?).with(user.id).and_return(true)
+  end
+
+  describe "validate unchangeable attributes" do
+    context "when remindable changed" do
+      before do
+        reminder.remindable = build_stubbed(:work_package)
+      end
+
+      it_behaves_like "contract is invalid", base: :unchangeable
+    end
+
+    context "when creator_id changed" do
+      before do
+        new_creator = build_stubbed(:user)
+        reminder.creator = new_creator
+        allow(User).to receive(:exists?).with(new_creator.id).and_return(true)
+      end
+
+      it_behaves_like "contract is invalid", base: :unchangeable
+    end
+  end
+
+  include_examples "contract reuses the model errors"
+end
diff --git a/spec/factories/reminders_factory.rb b/spec/factories/reminders_factory.rb
new file mode 100644
index 000000000000..0c195743a1e9
--- /dev/null
+++ b/spec/factories/reminders_factory.rb
@@ -0,0 +1,62 @@
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+FactoryBot.define do
+  factory :reminder do
+    remindable factory: :work_package
+    creator factory: :user
+    remind_at { 1.day.from_now }
+    note { "This is a reminder" }
+
+    trait :scheduled do
+      job_id { SecureRandom.uuid }
+    end
+
+    trait :completed do
+      job_id { SecureRandom.uuid }
+      completed_at { Time.zone.now }
+    end
+
+    trait :with_unread_notifications do
+      after(:create) do |reminder|
+        create(:reminder_notification, reminder:, notification: create(:notification, read_ian: false))
+      end
+    end
+
+    trait :with_read_notifications do
+      after(:create) do |reminder|
+        create(:reminder_notification, reminder:, notification: create(:notification, read_ian: true))
+      end
+    end
+  end
+
+  factory :reminder_notification do
+    reminder
+    notification
+  end
+end
diff --git a/spec/models/concerns/remindable_spec.rb b/spec/models/concerns/remindable_spec.rb
new file mode 100644
index 000000000000..c86420aa8f73
--- /dev/null
+++ b/spec/models/concerns/remindable_spec.rb
@@ -0,0 +1,37 @@
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+require "spec_helper"
+
+RSpec.describe Remindable do
+  let(:remindable) { build_stubbed(:work_package) }
+
+  describe "Associations" do
+    it { expect(remindable).to have_many(:reminders) }
+  end
+end
diff --git a/spec/models/notification_spec.rb b/spec/models/notification_spec.rb
index 7e9c73044222..c21c920e2617 100644
--- a/spec/models/notification_spec.rb
+++ b/spec/models/notification_spec.rb
@@ -28,6 +28,40 @@
 require "spec_helper"
 
 RSpec.describe Notification do
+  describe "Associations" do
+    it { is_expected.to belong_to(:journal) }
+    it { is_expected.to belong_to(:resource) }
+    it { is_expected.to belong_to(:actor).class_name("User") }
+    it { is_expected.to belong_to(:recipient).class_name("User") }
+
+    it { is_expected.to have_one(:reminder_notification).dependent(:destroy) }
+    it { is_expected.to have_one(:reminder).through(:reminder_notification) }
+  end
+
+  describe "Enums" do
+    it do
+      expect(subject).to define_enum_for(:reason)
+        .with_values(
+          mentioned: 0,
+          assigned: 1,
+          watched: 2,
+          subscribed: 3,
+          commented: 4,
+          created: 5,
+          processed: 6,
+          prioritized: 7,
+          scheduled: 8,
+          responsible: 9,
+          date_alert_start_date: 10,
+          date_alert_due_date: 11,
+          shared: 12,
+          reminder: 13
+        )
+        .with_prefix
+        .backed_by_column_of_type(:integer)
+    end
+  end
+
   describe ".save" do
     context "for a non existing journal (e.g. because it has been deleted)" do
       let(:notification) { build(:notification) }
diff --git a/spec/models/reminder_notification_spec.rb b/spec/models/reminder_notification_spec.rb
new file mode 100644
index 000000000000..95c8193813c2
--- /dev/null
+++ b/spec/models/reminder_notification_spec.rb
@@ -0,0 +1,36 @@
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+require "spec_helper"
+
+RSpec.describe ReminderNotification do
+  describe "Associations" do
+    it { is_expected.to belong_to(:reminder) }
+    it { is_expected.to belong_to(:notification) }
+  end
+end
diff --git a/spec/models/reminder_spec.rb b/spec/models/reminder_spec.rb
new file mode 100644
index 000000000000..3c3a9c675a7a
--- /dev/null
+++ b/spec/models/reminder_spec.rb
@@ -0,0 +1,95 @@
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+require "spec_helper"
+
+RSpec.describe Reminder do
+  describe "Associations" do
+    it { is_expected.to belong_to(:remindable) }
+    it { is_expected.to belong_to(:creator).class_name("User") }
+    it { is_expected.to have_many(:reminder_notifications).dependent(:destroy) }
+    it { is_expected.to have_many(:notifications).through(:reminder_notifications) }
+  end
+
+  describe "#unread_notifications?" do
+    context "with an unread notification" do
+      subject { create(:reminder, :with_unread_notifications) }
+
+      it { is_expected.to be_an_unread_notification }
+      it { expect(subject.unread_notifications).to be_present }
+    end
+
+    context "with no unread notifications" do
+      subject { create(:reminder, :with_read_notifications) }
+
+      it { is_expected.not_to be_an_unread_notification }
+      it { expect(subject.unread_notifications).to be_empty }
+    end
+
+    context "with no notifications" do
+      subject { build_stubbed(:reminder) }
+
+      it { is_expected.not_to be_an_unread_notification }
+      it { expect(subject.unread_notifications).to be_empty }
+    end
+  end
+
+  describe "#scheduled?" do
+    it "returns true if job_id is present" do
+      reminder = build_stubbed(:reminder, :scheduled)
+
+      expect(reminder).to be_scheduled
+    end
+
+    it "returns false if job_id is not present" do
+      reminder = build(:reminder, job_id: nil)
+
+      expect(reminder).not_to be_scheduled
+    end
+
+    it "returns false if completed_at is present" do
+      reminder = build(:reminder, :scheduled, :completed)
+
+      expect(reminder).not_to be_scheduled
+    end
+  end
+
+  describe "#completed?" do
+    it "returns true if completed_at is present" do
+      reminder = build(:reminder, :completed)
+
+      expect(reminder).to be_completed
+    end
+
+    it "returns false if completed_at is not present" do
+      reminder = build(:reminder, completed_at: nil)
+
+      expect(reminder).not_to be_completed
+    end
+  end
+end
diff --git a/spec/services/reminders/create_service_spec.rb b/spec/services/reminders/create_service_spec.rb
new file mode 100644
index 000000000000..b220ee90aa75
--- /dev/null
+++ b/spec/services/reminders/create_service_spec.rb
@@ -0,0 +1,52 @@
+# frozen_string_literal: true
+
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+require "spec_helper"
+require "services/base_services/behaves_like_create_service"
+
+RSpec.describe Reminders::CreateService do
+  it_behaves_like "BaseServices create service" do
+    let(:factory) { :reminder }
+
+    before do
+      allow(model_instance).to receive(:update_columns).and_return(true)
+      allow(Reminders::ScheduleReminderJob).to receive(:schedule)
+        .with(model_instance)
+        .and_return(instance_double(Reminders::ScheduleReminderJob, job_id: 1))
+    end
+
+    it "schedules a reminder job" do
+      subject
+
+      expect(Reminders::ScheduleReminderJob).to have_received(:schedule).with(model_instance)
+      expect(model_instance).to have_received(:update_columns).with(job_id: 1)
+    end
+  end
+end
diff --git a/spec/services/reminders/delete_service_spec.rb b/spec/services/reminders/delete_service_spec.rb
new file mode 100644
index 000000000000..40607fecb3c9
--- /dev/null
+++ b/spec/services/reminders/delete_service_spec.rb
@@ -0,0 +1,98 @@
+# frozen_string_literal: true
+
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+require "spec_helper"
+require "services/base_services/behaves_like_delete_service"
+
+RSpec.describe Reminders::DeleteService do
+  it_behaves_like "BaseServices delete service" do
+    let(:factory) { :reminder }
+
+    before do
+      allow(model_instance).to receive(:update).and_return(model_destroy_result)
+    end
+  end
+
+  describe "Remove reminder" do
+    subject { described_class.new(user:, model: model_instance).call }
+
+    let(:model_instance) { create(:reminder, :scheduled, :with_unread_notifications, creator: user) }
+    let(:user) { create(:admin) }
+
+    context "with an existing unfinished scheduled job" do
+      let(:job) { instance_double(GoodJob::Job, finished?: false, destroy: true) }
+
+      before do
+        model_instance.update(job_id: 1, completed_at: nil)
+        allow(GoodJob::Job).to receive(:find_by).and_return(job)
+      end
+
+      it "completes the reminder" do
+        expect { subject }.to change(model_instance, :completed_at).from(nil)
+
+        aggregate_failures "destroy existing job" do
+          expect(GoodJob::Job).to have_received(:find_by).with(id: "1")
+          expect(job).to have_received(:destroy)
+        end
+
+        aggregate_failures "marks unread notifications as read" do
+          expect(model_instance.notifications.count).to eq(1)
+          expect(model_instance.unread_notifications.count).to eq(0)
+        end
+
+        aggregate_failures "marks the reminder as complete" do
+          expect(model_instance).to be_completed
+        end
+      end
+    end
+
+    context "with an existing finished scheduled job" do
+      let(:job) { instance_double(GoodJob::Job, finished?: true, destroy: true) }
+
+      before do
+        model_instance.update(job_id: 1, completed_at: nil)
+        allow(GoodJob::Job).to receive(:find_by).and_return(job)
+      end
+
+      it "completes the reminder" do
+        expect { subject }.to change(model_instance, :completed_at).from(nil)
+
+        aggregate_failures "does NOT destroy existing job" do
+          expect(GoodJob::Job).to have_received(:find_by).with(id: "1")
+          expect(job).not_to have_received(:destroy)
+        end
+
+        aggregate_failures "marks the reminder as complete" do
+          expect(model_instance).to be_completed
+        end
+      end
+    end
+  end
+end
diff --git a/spec/services/reminders/update_service_spec.rb b/spec/services/reminders/update_service_spec.rb
new file mode 100644
index 000000000000..be14bd68b154
--- /dev/null
+++ b/spec/services/reminders/update_service_spec.rb
@@ -0,0 +1,149 @@
+# frozen_string_literal: true
+
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+require "spec_helper"
+require "services/base_services/behaves_like_update_service"
+
+RSpec.describe Reminders::UpdateService do
+  it_behaves_like "BaseServices update service" do
+    let(:factory) { :reminder }
+  end
+
+  describe "remind_at changed" do
+    subject { described_class.new(user:, model: model_instance).call(call_attributes) }
+
+    let(:model_instance) { create(:reminder, :scheduled, :with_unread_notifications, creator: user) }
+    let(:user) { create(:admin) }
+    let(:call_attributes) { { remind_at: 2.days.from_now } }
+
+    before do
+      model_instance.update(job_id: 1)
+      allow(Reminders::ScheduleReminderJob).to receive(:schedule)
+        .with(model_instance)
+        .and_return(instance_double(Reminders::ScheduleReminderJob, job_id: 2))
+    end
+
+    context "with an existing unfinished scheduled job" do
+      let(:job) { instance_double(GoodJob::Job, finished?: false, destroy: true) }
+
+      before do
+        allow(GoodJob::Job).to receive(:find_by).and_return(job)
+      end
+
+      it "reschedules the reminder" do
+        expect { subject }.to change(model_instance, :job_id).from("1").to("2")
+
+        aggregate_failures "destroy existing job" do
+          expect(GoodJob::Job).to have_received(:find_by).with(id: "1")
+          expect(job).to have_received(:destroy)
+        end
+
+        aggregate_failures "marks unread notifications as read" do
+          expect(model_instance.notifications.count).to eq(1)
+          expect(model_instance.unread_notifications.count).to eq(0)
+        end
+
+        aggregate_failures "schedule new job" do
+          expect(model_instance.remind_at.to_i).to eq(call_attributes[:remind_at].to_i)
+          expect(Reminders::ScheduleReminderJob).to have_received(:schedule).with(model_instance)
+        end
+      end
+    end
+
+    context "with an existing finished scheduled job" do
+      let(:job) { instance_double(GoodJob::Job, finished?: true, destroy: true) }
+
+      before do
+        allow(GoodJob::Job).to receive(:find_by).and_return(job)
+      end
+
+      it "schedules a new job" do
+        expect { subject }.to change(model_instance, :job_id).from("1").to("2")
+
+        aggregate_failures "does NOT destroy existing job" do
+          expect(GoodJob::Job).to have_received(:find_by).with(id: "1")
+          expect(job).not_to have_received(:destroy)
+        end
+
+        aggregate_failures "schedule new job" do
+          expect(model_instance.remind_at.to_i).to eq(call_attributes[:remind_at].to_i)
+          expect(Reminders::ScheduleReminderJob).to have_received(:schedule).with(model_instance)
+        end
+      end
+    end
+
+    context "with remind_at attribute in non-utc timezone" do
+      let(:call_attributes) { { remind_at: 2.days.from_now.in_time_zone("Africa/Nairobi") } }
+
+      it "reschedules the reminder" do
+        expect { subject }.to change(model_instance, :job_id).from("1").to("2")
+
+        aggregate_failures "schedule new job" do
+          expect(model_instance.remind_at.to_i).to eq(call_attributes[:remind_at].to_i)
+          expect(Reminders::ScheduleReminderJob).to have_received(:schedule).with(model_instance)
+        end
+      end
+    end
+  end
+
+  describe "unchangeable attributes" do
+    let(:original_creator) { create(:user) }
+    let(:original_remindable) { create(:work_package) }
+    let(:model_instance) { create(:reminder, creator: original_creator, remindable: original_remindable) }
+
+    context "when attempting to update the creator" do
+      subject { described_class.new(user: model_instance.creator, model: model_instance).call(creator: another_user) }
+
+      let(:another_user) { create(:user) }
+
+      it "does not update the creator", :aggregate_failures do
+        update_svc = subject
+
+        expect(update_svc).to be_a_failure
+        expect(update_svc.result.reload.creator).to eq(original_creator)
+        expect(update_svc.message).to eq("Creator is invalid. may not be accessed. cannot be changed.")
+      end
+    end
+
+    context "when attempting to update the remindable" do
+      subject { described_class.new(user: model_instance.creator, model: model_instance).call(remindable: another_remindable) }
+
+      let(:another_remindable) { create(:work_package) }
+
+      it "does not update the remindable", :aggregate_failures do
+        update_svc = subject
+
+        expect(update_svc).to be_a_failure
+        expect(update_svc.result.reload.remindable).to eq(original_remindable)
+        expect(update_svc.message).to include("cannot be changed.")
+      end
+    end
+  end
+end
diff --git a/spec/workers/reminders/schedule_reminder_job_spec.rb b/spec/workers/reminders/schedule_reminder_job_spec.rb
new file mode 100644
index 000000000000..2928e20cb68a
--- /dev/null
+++ b/spec/workers/reminders/schedule_reminder_job_spec.rb
@@ -0,0 +1,77 @@
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+require "spec_helper"
+
+RSpec.describe Reminders::ScheduleReminderJob do
+  describe ".schedule" do
+    let(:reminder) { create(:reminder) }
+
+    subject { described_class.schedule(reminder) }
+
+    it "enqueues a ScheduleReminderJob" do
+      expect { subject }
+        .to have_enqueued_job(described_class)
+              .at(reminder.remind_at)
+              .with(reminder)
+    end
+  end
+
+  describe "#perform" do
+    let(:reminder) { create(:reminder) }
+
+    subject { described_class.new.perform(reminder) }
+
+    it "creates a notification from the reminder" do
+      notification_svc = nil
+      expect { notification_svc = subject }.to change(Notification, :count).by(1) & change(ReminderNotification, :count).by(1)
+
+      aggregate_failures "notification attributes" do
+        notification = notification_svc.result
+
+        expect(notification.recipient_id).to eq(reminder.creator_id)
+        expect(notification.resource).to eq(reminder.remindable)
+        expect(notification.reason).to eq("reminder")
+      end
+
+      aggregate_failures "marks reminder as having unread notifications" do
+        expect(reminder.reload).to be_an_unread_notification
+      end
+    end
+
+    context "when the reminder is already notified" do
+      before do
+        create(:reminder_notification, reminder: reminder, notification: create(:notification, read_ian: false))
+      end
+
+      it "does not create a notification from the reminder" do
+        expect { subject }.not_to change(Notification, :count)
+      end
+    end
+  end
+end