diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index c3d420c0c..d63058fa6 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -17,6 +17,9 @@ jobs:
           toolchain: stable
           profile: minimal
           components: rustfmt, clippy
+          default: true
+      - uses: Swatinem/rust-cache@v1
+        continue-on-error: true
       - env:
           CLIPPYFLAGS: --deny warnings --allow clippy::needless-lifetimes
         run: |
@@ -27,50 +30,67 @@ jobs:
   test:
     name: python${{ matrix.python-version }}-${{ matrix.platform.python-architecture }} ${{ matrix.platform.os }}
     runs-on: ${{ matrix.platform.os }}
+    needs: [lint, check-msrv, linalg-example]
     strategy:
-      max-parallel: 16
+      fail-fast: false
       matrix:
-        python-version: [3.6, 3.7, 3.8, 3.9]
+        python-version: [3.7, 3.8, 3.9]
         platform: [
           { os: "ubuntu-latest", python-architecture: "x64", rust-target: "x86_64-unknown-linux-gnu" },
           { os: "macOS-latest",   python-architecture: "x64", rust-target: "x86_64-apple-darwin" },
           { os: "windows-latest", python-architecture: "x64", rust-target: "x86_64-pc-windows-msvc" },
           { os: "windows-latest", python-architecture: "x86", rust-target: "i686-pc-windows-msvc" },
         ]
+        include:
+          # NumPy does not provide pre-built wheels for PyPy on macOS and Windows
+          - python-version: pypy-3.7
+            platform: { os: "ubuntu-latest", python-architecture: "x64", rust-target: "x86_64-unknown-linux-gnu" }
+          - python-version: pypy-3.8
+            platform: { os: "ubuntu-latest", python-architecture: "x64", rust-target: "x86_64-unknown-linux-gnu" }
     steps:
       - uses: actions/checkout@v2
       - name: Set up Python ${{ matrix.python-version }}
         uses: actions/setup-python@v2
         with:
           python-version: ${{ matrix.python-version }}
+          architecture: ${{ matrix.platform.python-architecture }}
       - name: Install Rust
         uses: actions-rs/toolchain@v1
         with:
           toolchain: stable
+          profile: minimal
+          target: ${{ matrix.platform.rust-target }}
           default: true
-      - run: rustup set default-host ${{ matrix.platform.rust-target }}
+      - name: Install toml
+        run: pip install toml
+      - name: Edit Cargo.toml and enable new resolver
+        run: |
+          import toml
+          cargo_toml = toml.load("Cargo.toml")
+          cargo_toml["workspace"]["resolver"] = "2"
+          with open("Cargo.toml", "w") as f:
+            toml.dump(cargo_toml, f)
+        shell: python
       - name: Build without default features
-        run: cargo build --no-default-features --verbose
+        run: cargo build --no-default-features
       - name: Build with default features
-        run: cargo build --verbose
-      - name: Install test dependencies
+        run: cargo build
+      - name: Test
         run: |
-          python -m pip install --upgrade pip
-          pip install maturin numpy poetry
-      - name: Run cargo test
-        run: cargo test --verbose
-      - name: Test Examples
+            pip install numpy
+            cargo test
+        # Not on PyPy, because no embedding API
+        if: ${{ !startsWith(matrix.python-version, 'pypy') }}
+      - name: Test example
         run: |
-          for example_dir in 'examples/simple-extension'; do
-              pushd $example_dir && \
-                poetry install && \
-                poetry run maturin develop && \
-                poetry run pytest && \
-                popd
-          done
-        shell: bash
+          pip install tox
+          tox
+        working-directory: examples/simple-extension
     env:
+      CARGO_TERM_VERBOSE: true
+      CARGO_BUILD_TARGET: ${{ matrix.platform.rust-target }}
       RUST_BACKTRACE: 1
+      TOX_TESTENV_PASSENV: CARGO_BUILD_TARGET
 
   check-msrv:
     runs-on: ubuntu-latest
@@ -80,37 +100,48 @@ jobs:
         uses: actions/setup-python@v2
         with:
           python-version: 3.8
-      - name: Install MSRV Rust
+      - name: Install Rust
         uses: actions-rs/toolchain@v1
         with:
-          profile: minimal
           toolchain: 1.48.0
+          profile: minimal
           default: true
-      - name: Install maturin, poetry, and toml
-        run: pip install maturin poetry toml
-      - name: Create an isolated example directory
-        run: cp -r examples/simple-extension/ ../simple-extension-msrv
-      - name: Edit Cargo.toml and change the path of rust-numpy
+      - uses: Swatinem/rust-cache@v1
+        with:
+          working-directory: examples/simple-extension
+        continue-on-error: true
+      - name: Install toml
+        run: pip install toml
+      - name: Edit Cargo.toml and detach from workspace
         run: |
           import toml
           cargo_toml = toml.load("Cargo.toml")
-          cargo_toml["dependencies"]["numpy"]["path"] = "../rust-numpy"
           cargo_toml["dependencies"]["ndarray"] = "0.13.1"
           cargo_toml["dependencies"]["num-complex"] = "0.2.4"
+          cargo_toml["workspace"] = {}
           with open("Cargo.toml", "w") as f:
             toml.dump(cargo_toml, f)
-        working-directory: ../simple-extension-msrv
+        working-directory: examples/simple-extension
         shell: python
-      - name: Use ndarray 0.13.1
+      - name: Generate lockfile
+        run: cargo generate-lockfile
+        working-directory: examples/simple-extension
+      - name: Unify dependencies on ndarray to 0.13.1
         run: |
-          cargo generate-lockfile
-          cargo update -p $(cargo pkgid -p ndarray 2>&1 >/dev/null | grep 0.15 | sed -e 's/^[ \t]*//') --precise 0.13.1
-        working-directory: ../simple-extension-msrv
-      - name: Test Example
+          import toml
+          import subprocess
+          cargo_lock = toml.load("Cargo.lock")
+          for pkg in cargo_lock["package"]:
+            if pkg["name"] == "ndarray" and pkg["version"] != "0.13.1":
+              pkg_id = pkg["name"] + ":" + pkg["version"]
+              subprocess.run(["cargo", "update", "--package", pkg_id, "--precise", "0.13.1"], check=True)
+        working-directory: examples/simple-extension
+        shell: python
+      - name: Test example
         run: |
-          poetry install && poetry run maturin develop && poetry run pytest
-        working-directory: ../simple-extension-msrv
-        shell: bash
+          pip install tox
+          tox
+        working-directory: examples/simple-extension
 
   linalg-example:
     runs-on: ubuntu-latest
@@ -120,18 +151,18 @@ jobs:
         uses: actions/setup-python@v2
         with:
           python-version: 3.8
-      - name: Install gfortran
-        run: |
-          sudo apt install -y gfortran
+      - name: Install OpenBLAS
+        run: sudo apt install --yes libopenblas-dev
       - name: Install Rust
         uses: actions-rs/toolchain@v1
         with:
           toolchain: stable
-      - name: Install maturin and poetry
-        run: pip install maturin poetry
-      - name: Test Examples
+          profile: minimal
+          default: true
+      - uses: Swatinem/rust-cache@v1
+        continue-on-error: true
+      - name: Test example
         run: |
-          cd examples/linalg && \
-            poetry install && \
-            poetry run maturin develop && \
-            poetry run pytest
+          pip install tox
+          tox
+        working-directory: examples/linalg
diff --git a/.gitignore b/.gitignore
index 95947331d..e6c70b047 100644
--- a/.gitignore
+++ b/.gitignore
@@ -14,4 +14,4 @@ build/
 *.so
 *.egg-info/
 **/dist/
-__pycache__
\ No newline at end of file
+__pycache__
diff --git a/examples/linalg/Cargo.toml b/examples/linalg/Cargo.toml
index 549dfe413..da4c504b0 100644
--- a/examples/linalg/Cargo.toml
+++ b/examples/linalg/Cargo.toml
@@ -11,4 +11,4 @@ crate-type = ["cdylib"]
 [dependencies]
 pyo3 = { version = "0.15", features = ["extension-module"] }
 numpy = { path = "../.." }
-ndarray-linalg = { version = "0.14.1", features = ["openblas-static"] }
+ndarray-linalg = { version = "0.14.1", features = ["openblas-system"] }
diff --git a/examples/linalg/poetry.lock b/examples/linalg/poetry.lock
deleted file mode 100644
index 741d7cde9..000000000
--- a/examples/linalg/poetry.lock
+++ /dev/null
@@ -1,235 +0,0 @@
-[[package]]
-name = "atomicwrites"
-version = "1.4.0"
-description = "Atomic file writes."
-category = "dev"
-optional = false
-python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*"
-
-[[package]]
-name = "attrs"
-version = "20.3.0"
-description = "Classes Without Boilerplate"
-category = "dev"
-optional = false
-python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*"
-
-[package.extras]
-dev = ["coverage[toml] (>=5.0.2)", "hypothesis", "pympler", "pytest (>=4.3.0)", "six", "zope.interface", "furo", "sphinx", "pre-commit"]
-docs = ["furo", "sphinx", "zope.interface"]
-tests = ["coverage[toml] (>=5.0.2)", "hypothesis", "pympler", "pytest (>=4.3.0)", "six", "zope.interface"]
-tests_no_zope = ["coverage[toml] (>=5.0.2)", "hypothesis", "pympler", "pytest (>=4.3.0)", "six"]
-
-[[package]]
-name = "colorama"
-version = "0.4.4"
-description = "Cross-platform colored terminal text."
-category = "dev"
-optional = false
-python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*"
-
-[[package]]
-name = "importlib-metadata"
-version = "3.1.1"
-description = "Read metadata from Python packages"
-category = "dev"
-optional = false
-python-versions = ">=3.6"
-
-[package.dependencies]
-zipp = ">=0.5"
-
-[package.extras]
-docs = ["sphinx", "jaraco.packaging (>=3.2)", "rst.linker (>=1.9)"]
-testing = ["pytest (>=3.5,!=3.7.3)", "pytest-checkdocs (>=1.2.3)", "pytest-flake8", "pytest-cov", "jaraco.test (>=3.2.0)", "packaging", "pep517", "pyfakefs", "flufl.flake8", "pytest-black (>=0.3.7)", "pytest-mypy", "importlib-resources (>=1.3)"]
-
-[[package]]
-name = "iniconfig"
-version = "1.1.1"
-description = "iniconfig: brain-dead simple config-ini parsing"
-category = "dev"
-optional = false
-python-versions = "*"
-
-[[package]]
-name = "numpy"
-version = "1.19.4"
-description = "NumPy is the fundamental package for array computing with Python."
-category = "main"
-optional = false
-python-versions = ">=3.6"
-
-[[package]]
-name = "packaging"
-version = "20.7"
-description = "Core utilities for Python packages"
-category = "dev"
-optional = false
-python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*"
-
-[package.dependencies]
-pyparsing = ">=2.0.2"
-
-[[package]]
-name = "pluggy"
-version = "0.13.1"
-description = "plugin and hook calling mechanisms for python"
-category = "dev"
-optional = false
-python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*"
-
-[package.dependencies]
-importlib-metadata = {version = ">=0.12", markers = "python_version < \"3.8\""}
-
-[package.extras]
-dev = ["pre-commit", "tox"]
-
-[[package]]
-name = "py"
-version = "1.10.0"
-description = "library with cross-python path, ini-parsing, io, code, log facilities"
-category = "dev"
-optional = false
-python-versions = ">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*"
-
-[[package]]
-name = "pyparsing"
-version = "2.4.7"
-description = "Python parsing module"
-category = "dev"
-optional = false
-python-versions = ">=2.6, !=3.0.*, !=3.1.*, !=3.2.*"
-
-[[package]]
-name = "pytest"
-version = "6.1.2"
-description = "pytest: simple powerful testing with Python"
-category = "dev"
-optional = false
-python-versions = ">=3.5"
-
-[package.dependencies]
-atomicwrites = {version = ">=1.0", markers = "sys_platform == \"win32\""}
-attrs = ">=17.4.0"
-colorama = {version = "*", markers = "sys_platform == \"win32\""}
-importlib-metadata = {version = ">=0.12", markers = "python_version < \"3.8\""}
-iniconfig = "*"
-packaging = "*"
-pluggy = ">=0.12,<1.0"
-py = ">=1.8.2"
-toml = "*"
-
-[package.extras]
-checkqa_mypy = ["mypy (==0.780)"]
-testing = ["argcomplete", "hypothesis (>=3.56)", "mock", "nose", "requests", "xmlschema"]
-
-[[package]]
-name = "toml"
-version = "0.10.2"
-description = "Python Library for Tom's Obvious, Minimal Language"
-category = "dev"
-optional = false
-python-versions = ">=2.6, !=3.0.*, !=3.1.*, !=3.2.*"
-
-[[package]]
-name = "zipp"
-version = "3.4.0"
-description = "Backport of pathlib-compatible object wrapper for zip files"
-category = "dev"
-optional = false
-python-versions = ">=3.6"
-
-[package.extras]
-docs = ["sphinx", "jaraco.packaging (>=3.2)", "rst.linker (>=1.9)"]
-testing = ["pytest (>=3.5,!=3.7.3)", "pytest-checkdocs (>=1.2.3)", "pytest-flake8", "pytest-cov", "jaraco.test (>=3.2.0)", "jaraco.itertools", "func-timeout", "pytest-black (>=0.3.7)", "pytest-mypy"]
-
-[metadata]
-lock-version = "1.1"
-python-versions = ">=3.6"
-content-hash = "83547a5e762b65c813eca020324e3c5af1acba15f2c19cd0440408626194bbdd"
-
-[metadata.files]
-atomicwrites = [
-    {file = "atomicwrites-1.4.0-py2.py3-none-any.whl", hash = "sha256:6d1784dea7c0c8d4a5172b6c620f40b6e4cbfdf96d783691f2e1302a7b88e197"},
-    {file = "atomicwrites-1.4.0.tar.gz", hash = "sha256:ae70396ad1a434f9c7046fd2dd196fc04b12f9e91ffb859164193be8b6168a7a"},
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-]
-colorama = [
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diff --git a/examples/linalg/pyproject.toml b/examples/linalg/pyproject.toml
index 6753f95d9..193054ade 100644
--- a/examples/linalg/pyproject.toml
+++ b/examples/linalg/pyproject.toml
@@ -1,16 +1,3 @@
 [build-system]
 build-backend = "maturin"
-requires = ["poetry_core>=1.0.0"]
-
-[tool.poetry]
-name = "numpy-linalg-example"
-version = "0.1.0"
-description = "rust-numpy example with ndarray-linalg"
-authors = ["Yuji Kanagawa <yuji.kngw.80s.revive@gmail.com>"]
-
-[tool.poetry.dependencies]
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-python = ">=3.6"
-
-[tool.poetry.dev-dependencies]
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diff --git a/examples/linalg/tox.ini b/examples/linalg/tox.ini
new file mode 100644
index 000000000..c50b8b46c
--- /dev/null
+++ b/examples/linalg/tox.ini
@@ -0,0 +1,11 @@
+[tox]
+skipsdist = True
+
+[testenv]
+deps =
+    pip
+    numpy
+    pytest
+commands =
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+    pytest {posargs}
diff --git a/examples/simple-extension/poetry.lock b/examples/simple-extension/poetry.lock
deleted file mode 100644
index 741d7cde9..000000000
--- a/examples/simple-extension/poetry.lock
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-]
-pytest = [
-    {file = "pytest-6.1.2-py3-none-any.whl", hash = "sha256:4288fed0d9153d9646bfcdf0c0428197dba1ecb27a33bb6e031d002fa88653fe"},
-    {file = "pytest-6.1.2.tar.gz", hash = "sha256:c0a7e94a8cdbc5422a51ccdad8e6f1024795939cc89159a0ae7f0b316ad3823e"},
-]
-toml = [
-    {file = "toml-0.10.2-py2.py3-none-any.whl", hash = "sha256:806143ae5bfb6a3c6e736a764057db0e6a0e05e338b5630894a5f779cabb4f9b"},
-    {file = "toml-0.10.2.tar.gz", hash = "sha256:b3bda1d108d5dd99f4a20d24d9c348e91c4db7ab1b749200bded2f839ccbe68f"},
-]
-zipp = [
-    {file = "zipp-3.4.0-py3-none-any.whl", hash = "sha256:102c24ef8f171fd729d46599845e95c7ab894a4cf45f5de11a44cc7444fb1108"},
-    {file = "zipp-3.4.0.tar.gz", hash = "sha256:ed5eee1974372595f9e416cc7bbeeb12335201d8081ca8a0743c954d4446e5cb"},
-]
diff --git a/examples/simple-extension/pyproject.toml b/examples/simple-extension/pyproject.toml
index 958080afc..193054ade 100644
--- a/examples/simple-extension/pyproject.toml
+++ b/examples/simple-extension/pyproject.toml
@@ -1,16 +1,3 @@
 [build-system]
 build-backend = "maturin"
-requires = ["poetry_core>=1.0.0"]
-
-[tool.poetry]
-name = "numpy-example"
-version = "0.1.0"
-description = "A minimum example of rust-numpy"
-authors = ["Toshiki Teramura <toshiki.teramura@gmail.com>", "Yuji Kanagawa <yuji.kngw.80s.revive@gmail.com>"]
-
-[tool.poetry.dependencies]
-numpy = ">=1.18"
-python = ">=3.6"
-
-[tool.poetry.dev-dependencies]
-pytest = "^6.1"
+requires = ["maturin>=0.12,<0.13"]
diff --git a/examples/simple-extension/tox.ini b/examples/simple-extension/tox.ini
new file mode 100644
index 000000000..6b3ab2b9d
--- /dev/null
+++ b/examples/simple-extension/tox.ini
@@ -0,0 +1,11 @@
+[tox]
+skipsdist = True
+
+[testenv]
+deps =
+    pip
+    numpy
+    pytest
+commands =
+    python -m pip install .
+    pytest {posargs}