lighttpd (prescribed pronunciation: "lighty")[2] is an open-source web server optimized for speed-critical environments while remaining standards-compliant, secure and flexible.

[citation needed] It was originally written by Jan Kneschke as a proof-of-concept of the c10k problem – how to handle 10,000 connections in parallel on one server,[3] but has gained worldwide popularity.

The low memory footprint (compared to other web servers),[5] small CPU load and speed optimizations[6] make lighttpd suitable for servers that are suffering load problems, or for serving static media separately from dynamic content.

Lighttpd's FastCGI can be configured to support PHP with opcode caches (like APC) properly and efficiently.

Lighttpd also supports WebDNA, the resilient in-memory database system designed to build database-driven websites.