Yaws (Yet another web server) is a web server written in Erlang by Claes (klacke) Wikström. Yaws can be embedded into other Erlang-based applications or run as a regular standalone web server.
Because Yaws uses Erlang's lightweight threading system, it performs well under high concurrency. A load test conducted in 2002 comparing Yaws and Apache found that with the hardware tested, Apache 2.0.39 with the worker MPM failed at 4,000 concurrent connections, while Yaws continued functioning with over 80,000 concurrent connections.