Small, fast and free discussion board system written in PHP, can be based on any database supported by PHP.

A free web-based bulletin board system written in PHP with a variety of backend database option available.

Official site, offering news, support, and downloads of the forum software, modifications, and templates.

PunBB is a fast and lightweight PHP-powered discussion board.

A community software package with themes, fast message database, secure file-attaching system, and mod installation manager.

vBulletin is a powerful, scalable and fully customizable forums package for your web site.