The Apache HTTP Server Project is an effort to develop and maintain an open-source HTTP server for modern operating systems. (Apache)
Linux - FreeBSD - Windows - MAC OS X
lighttpd is a web server designed to be secure, fast, standards-compliant, and flexible while being optimized for speed-critical environments. (BSD)
Cross-platform
nginx is a lightweight, high performance web server/reverse proxy and e-mail (IMAP/POP3) proxy. (BSD)
Linux - FreeBSD - Windows - MAC OS X
3 applications