The C++ REST SDK (cpprestsdk) is a cross-platform, asynchronous C++ library for building cloud-based client-server applications. It provides a comprehensive set of APIs for HTTP client and server communication, JSON parsing and serialization, URI manipulation, WebSocket client support, OAuth 1.0 and 2.0 authentication, and asynchronous stream I/O. The library is built on a custom task-based concurrency model (PPLX) that abstracts platform-specific threading and synchronization, enabling portable async operations across Windows, Linux, macOS, iOS, and Android. The architecture is modular: HTTP client and server implementations use a pipeline stage pattern for middleware (e.g., compression, authentication), and the stream buffer abstraction decouples data sources from I/O operations. The codebase includes extensive functional tests using a bundled UnitTest++ framework, along with sample applications demonstrating real-world usage (BlackJack game, OAuth flows, file search). However, the repository is officially archived and no longer maintained; it exhibits significant technical drift, including deprecated APIs, platform-specific conditional compilation, and dependencies on older library versions (Boost, OpenSSL). Despite this, many components—such as the PPLX task system, URI builder, JSON value, and stream buffers—are well-crafted and could be extracted for reuse in new projects with minimal adaptation.