In Web 3.0 world the application comprize multiple services originated from different vendors. It is needed as for application vendor to help monetizing the application as for customers to consume various helpful or simply fun features like sharing, keeping notes, and zillion others.
The 3rd party (for application) feature vendors are giving an API to retrieve and post back the data. Some, in addition, provide the UI to be embedded into host application UI. This 3rd party UI presenting a microapplication which unlike full application meant to be used in context of host application, configured, and customized by host application (web page or native app UI).
Pagelet is a 1-page HTML micro front-end application capable of running as standalone web page or as embedded
( on front-end or back-end ) into another page.
Unlike microapplication the pagelet does not interact with external world say for keeping the data state. Container could provide the
persistence layer enabling the use of pagelet as microapplication in context of container.