libuv

libuv is a multi-platform C library that provides asynchronous I/O and a cross-platform event loop. It is designed to help developers write scalable, non-blocking I/O code across operating systems.

It offers a unified API for file system access, network sockets, pipes, DNS resolution, timers, and subprocesses. The core is a single event loop, uv_loop_t, that coordinates events and callbacks. For CPU-bound work, it provides a thread pool accessible via uv_queue_work calls. It also handles signals and idle tasks.

The library abstracts OS-specific mechanisms such as epoll, kqueue, IOCP, and select into a consistent API, enabling portable behavior on Windows, macOS, Linux, and BSDs. It uses handles and streams (uv_handle_t, uv_stream_t) to model resources.

Node.js popularized libuv as its cross-platform I/O layer; since then libuv has been adopted by other projects and language bindings, including lightweight runtimes and tooling. It is maintained as an open-source project with contributions from a broad community.

Released under a permissive open-source license, libuv development occurs on GitHub with open governance and broad community involvement.