The Windows App SDK (formerly Project Reunion) is a Microsoft platform SDK for building modern Windows desktop applications. It provides a unified set of WinRT APIs and runtime components that bridge Win32 and UWP development, enabling features like app lifecycle management (single-instance, file/protocol activation), dynamic package dependencies (resolving framework packages at runtime), rich notifications (toast, push, badge), resource management via MRT Core (PRI files with qualifier-based selection), deployment APIs (package sets, validation), environment variable management, OAuth 2.0 authentication, and interop wrappers for storage pickers and camera capture. The architecture is modular: each feature area is implemented as a separate C++/WinRT component (DLL) that can be consumed individually via NuGet packages. The SDK supports both packaged (MSIX) and unpackaged (self-contained) apps, with a bootstrap DLL that initializes the runtime and hooks into the Windows package graph via Detours. Key entry points include MddBootstrapInitialize2 for runtime initialization, the WindowsAppRuntime DLL for COM class factories, and individual component APIs like AppNotificationManager, PushNotificationManager, and PackageDependency. External dependencies include the Windows SDK, C++/WinRT projections, the Windows Implementation Libraries (WIL), and Microsoft Detours for API interception. Data flows involve inter-process communication through shared memory (for activation redirection), named pipes (for OAuth callbacks), and COM out-of-process servers (for push notification long-running tasks). The codebase is heavily instrumented with TraceLogging telemetry and uses feature flags (TerminalVelocity) to gate experimental APIs.
This repository is a vast collection of over 1,800 sample projects demonstrating nearly every feature of the Universal Windows Platform (UWP) SDK. It is not a single application but an educational resource containing hundreds of independent, self-contained samples covering sensors, cameras, networking, graphics, file access, notifications, background tasks, device interactions, and many other Windows APIs. Each sample follows a consistent architectural pattern: a MainPage with a scenario selector and multiple Scenario pages that illustrate specific API usage in C++/CX, C++/WinRT, C#, and occasional JavaScript (largely archived). The samples are designed to be built and run with Visual Studio on Windows 10 and 11, serving as both a learning tool for developers and a reference for API behavior. The codebase is extensive and fairly well-organized by feature area, but it suffers from significant technical drift. Many archived samples use deprecated technologies such as C++/CX (legacy) and WinJS (JavaScript), while newer samples adopt modern C++/WinRT. This inconsistency means that some samples may not compile or behave correctly on the latest Windows SDK without updates. Additionally, the repository lacks a unified build system or automated testing, and it includes a large amount of boilerplate code (e.g., identical SampleConfiguration files across hundreds of projects). Despite these drawbacks, the repository remains actively maintained by Microsoft (last commit within 30 days) and provides genuine value for understanding UWP APIs, with several reusable utility components buried within the samples.