Threaded or linear viewing of posts, address books, CSS compatible, session or cookie based, moderators, multi-language support, private forums, profanity filter, and user pictures. [Commercial]

PHP/MySQL forum developed by Umakant Patil that includes group permissions, IP banning, and anti-spam measures.

Unicode-supporting PHP/MySQL forum software that produces standard XHTML and CSS. [Open source, GPL]

PHP/MySQL forum software that's hosted remotely and customizable.

Interoperable (vBulletin, phpBB2 and IPB) Web/WAP Discussion Forums for Cell phones, PDAs and other handheld devices.

Commercial PHP forum software based on WowBB that offers a WYSIWYG editor and uses MySQL

Fully customizable, extensible and translateable PHP/MySQL forum script. [Commercial]