Lighttpd (or "lighty") is secure, fast, flexible and high performance web server software developed in 2003 by Jan Kneschke as a proof-of-concept to solve the c10k problem.
It is free software written in C and distributed under the terms of the BSD license.
Its speed comes from the fact that it has a smaller memory footprint than other HTTP servers as well as intelligent management of the CPU load.
The main disadvantage of lighttpd compared to its competitor Apache is that it does not support .htaccess files: directives are only evaluated once, when the server starts up, and need to be restarted in order to be taken into account.
Lighttpd used by large sites like YouTube, SourceForge.net, or Wikipedia's image server. It is in 7th position of the most used web servers according to the Netcraft study. It is part of the software supplied with the Fedora distribution.
lighttpd supports the FastCGI, SCGI and CGI interfaces to external programs, allowing web applications written in any programming language to be used with the server. As a particularly popular language, PHP performance has received special attention. Lighttpd's FastCGI can be configured to support PHP with opcode caches (like APC) properly and efficiently. Additionally, it has received attention from its popularity within the Python, Perl, Ruby and Lua communities.
Lighttpd also supports WebDNA, the resilient in-memory database system designed to build database-driven websites. It is a popular web server for the Catalyst and Ruby on Rails web frameworks. Lighttpd does not support ISAPI.