diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 00000000..62ae5d24
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,142 @@
+name: CI
+
+on:
+  push:
+    branches: [develop, main]
+  pull_request:
+    branches: [develop, main]
+  workflow_dispatch:
+
+jobs:
+  linux:
+    name: Linux GCC ${{ matrix.build_type }}
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        build_type: [Debug, Release]
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Configure
+        run: cmake -B build -DCMAKE_BUILD_TYPE=${{ matrix.build_type }}
+
+      - name: Build
+        run: cmake --build build -j
+
+      - name: Test
+        run: ctest --test-dir build --output-on-failure
+
+  macos:
+    name: macOS AppleClang ${{ matrix.build_type }}
+    runs-on: macos-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        build_type: [Debug, Release]
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Configure
+        run: cmake -B build -DCMAKE_BUILD_TYPE=${{ matrix.build_type }}
+
+      - name: Build
+        run: cmake --build build -j
+
+      - name: Test
+        run: ctest --test-dir build --output-on-failure
+
+  linux-sanitizers:
+    name: Linux GCC ASAN+UBSAN ${{ matrix.build_type }}
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        build_type: [Debug, Release]
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Configure
+        run: cmake -B build -DCMAKE_BUILD_TYPE=${{ matrix.build_type }} -DENABLE_ADDRESS_SANITIZER=ON -DENABLE_UNDEFINED_SANITIZER=ON
+
+      - name: Build
+        run: cmake --build build -j
+
+      - name: Test
+        run: ctest --test-dir build --output-on-failure
+
+  macos-sanitizers:
+    name: macOS AppleClang ASAN+UBSAN ${{ matrix.build_type }}
+    runs-on: macos-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        build_type: [Debug, Release]
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Configure
+        run: cmake -B build -DCMAKE_BUILD_TYPE=${{ matrix.build_type }} -DENABLE_ADDRESS_SANITIZER=ON -DENABLE_UNDEFINED_SANITIZER=ON
+
+      - name: Build
+        run: cmake --build build -j
+
+      - name: Test
+        run: ctest --test-dir build --output-on-failure
+
+  windows:
+    name: Windows MSVC ${{ matrix.build_type }}
+    runs-on: windows-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        build_type: [Debug, Release]
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Configure
+        run: cmake -B build
+
+      - name: Build
+        run: cmake --build build --config ${{ matrix.build_type }} -j
+
+      - name: Test
+        run: ctest --test-dir build --output-on-failure -C ${{ matrix.build_type }}
+
+  linux-tsan:
+    name: Linux GCC TSAN ${{ matrix.build_type }}
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        build_type: [Debug, Release]
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Configure
+        run: cmake -B build -DCMAKE_BUILD_TYPE=${{ matrix.build_type }} -DENABLE_THREAD_SANITIZER=ON
+
+      - name: Build
+        run: cmake --build build -j
+
+      - name: Test
+        run: ctest --test-dir build --output-on-failure
+
+  macos-tsan:
+    name: macOS AppleClang TSAN ${{ matrix.build_type }}
+    runs-on: macos-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        build_type: [Debug, Release]
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Configure
+        run: cmake -B build -DCMAKE_BUILD_TYPE=${{ matrix.build_type }} -DENABLE_THREAD_SANITIZER=ON
+
+      - name: Build
+        run: cmake --build build -j
+
+      - name: Test
+        run: ctest --test-dir build --output-on-failure
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 878749ad..ad3e79a0 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -34,7 +34,7 @@ if(CMAKE_COMPILER_IS_GNUCC)
   endif()
 endif()
 
-if(CMAKE_COMPILER_IS_GNUCC OR "${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
+if(CMAKE_COMPILER_IS_GNUCC OR "${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang" OR "${CMAKE_CXX_COMPILER_ID}" STREQUAL "AppleClang")
   option(ENABLE_THREAD_SANITIZER "Enable thread sanitizer testing in gcc/clang" FALSE)
   if(ENABLE_THREAD_SANITIZER)
     add_definitions(-fsanitize=thread -g)
@@ -87,6 +87,16 @@ if(CMAKE_COMPILER_IS_GNUCC OR "${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
   endif()
 
 
+elseif(MSVC)
+  option(ENABLE_ADDRESS_SANITIZER "Enable address sanitizer testing in MSVC" FALSE)
+  if(ENABLE_ADDRESS_SANITIZER)
+    add_compile_options(/fsanitize=address)
+    # ASAN is incompatible with /RTC (runtime error checks) and incremental linking
+    string(REGEX REPLACE "/RTC[^ ]*" "" CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG}")
+    string(REGEX REPLACE "/RTC[^ ]*" "" CMAKE_C_FLAGS_DEBUG "${CMAKE_C_FLAGS_DEBUG}")
+    add_link_options(/INCREMENTAL:NO)
+  endif()
+
 endif()
 
 list(APPEND CPACK_SOURCE_IGNORE_FILES "${CMAKE_CURRENT_BINARY_DIR}")
diff --git a/appveyor.yml b/appveyor.yml
deleted file mode 100644
index 5a4fe67e..00000000
--- a/appveyor.yml
+++ /dev/null
@@ -1,23 +0,0 @@
-version: 6.1.x.{build}
-image:
-  - Visual Studio 2019
-environment:
-  matrix:
-  - VS_VERSION: "Visual Studio 16"
-build_script:
-- cmd: >-
-    mkdir build
-
-    cd build
-
-    cmake c:\Projects\chaiscript -G "%VS_VERSION%" -DBUILD_TESTING:BOOL=ON -DBUILD_MODULES:BOOL=ON
-
-    cmake --build . --config Debug
-test_script:
-- cmd: ctest -C Debug
-notifications:
-- provider: Webhook
-  url: https://webhooks.gitter.im/e/9ff725a985b5679d1d5d
-  on_build_success: true
-  on_build_failure: true
-  on_build_status_changed: false
diff --git a/include/chaiscript/language/chaiscript_common.hpp b/include/chaiscript/language/chaiscript_common.hpp
index 44116735..fb75a933 100644
--- a/include/chaiscript/language/chaiscript_common.hpp
+++ b/include/chaiscript/language/chaiscript_common.hpp
@@ -26,10 +26,6 @@
 
 namespace chaiscript {
   struct AST_Node;
-  struct AST_Node_Trace;
-  namespace exception {
-    struct eval_error;
-  }
 } // namespace chaiscript
 
 namespace chaiscript {
diff --git a/src/main.cpp b/src/main.cpp
index 6ec746fb..ab94b5d1 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -7,6 +7,7 @@
 // This is an open source non-commercial project. Dear PVS-Studio, please check it.
 // PVS-Studio Static Code Analyzer for C, C++ and C#: http://www.viva64.com
 
+#include <chrono>
 #include <iostream>
 #include <list>
 #include <regex>
diff --git a/unittests/compiled_tests.cpp b/unittests/compiled_tests.cpp
index d24590a9..3ba0732f 100644
--- a/unittests/compiled_tests.cpp
+++ b/unittests/compiled_tests.cpp
@@ -1501,3 +1501,23 @@ TEST_CASE("IO redirection different instances are independent") {
   CHECK(output1 == "from1");
   CHECK(output2 == "from2");
 }
+
+// Regression test for issue #607: AST_Node_Trace must be a complete type
+// when used in eval_error's std::vector<AST_Node_Trace> call_stack member.
+// This failed to compile with C++20 on clang/libc++ when AST_Node_Trace
+// was only forward-declared before eval_error's definition.
+TEST_CASE("eval_error with AST_Node_Trace call stack compiles in C++20") {
+  chaiscript::ChaiScript_Basic chai(create_chaiscript_stdlib(), create_chaiscript_parser());
+
+  // Trigger an eval_error by calling a non-existent function
+  try {
+    chai.eval("nonexistent_function()");
+    REQUIRE(false);
+  } catch (const chaiscript::exception::eval_error &e) {
+    // Verify that eval_error's call_stack member (std::vector<AST_Node_Trace>)
+    // is usable - this would fail to compile if AST_Node_Trace were incomplete
+    const auto &stack = e.call_stack;
+    CHECK(e.pretty_print().size() > 0);
+    (void)stack;
+  }
+}
diff --git a/unittests/now_function.chai b/unittests/now_function.chai
new file mode 100644
index 00000000..5825cdec
--- /dev/null
+++ b/unittests/now_function.chai
@@ -0,0 +1,3 @@
+// Regression test for issue #660: now() requires <chrono> include
+var t = now()
+assert_true(t > 0)