LIGHTTPD (pronounced by Lighty) is an opensource webserver for Security, Speed, compliance and flexibility. Its been optimized for high performance environments. With a small memory footprint, effective management of CPU load and advanced features like FastCGI, SCGI, Auth, Output compression and URL rewriting; lighttpd is the perfect solution for servers suffering from load problems.
lighttpd powers several popular Web 2.0 sites like YouTube, Wikipedia and Meebo. Its high speed io-infrastructure allows them to scale several times better with the same hardware than with alternative web-servers. Its event-driven architecture is optimized for a large number of parallel connections (keep-alive) which is important for high performance AJAX applications.
You can check the Lighty benchmark here.
You may be interested in some of the Lighty extension projects,
Lighty2Go – Portable Lighty webserver configured with MySQL and PHP stack.
yPortableWS – Portable Lighty Webserver with MySQL and PHP stack.
WLMP Project – Windows based Lighty with MySQL database server and PHP support.