Lighttpd ("lighty") is a fast open source web server, optimised for speed critical environments
Lighttpd (pronounced "lighty") is an open source web server optimised for speed critical environments, which is standards compliant. It attempts to be lower memory footprint, and more CPU efficient than other web servers, and is often simpler to configure. Initially it was targetted at static content, but now it is widely used for both static content and hosting CGI, PHP, Ruby, Python etc code.
More information is available on Wikipedia