http://www.getvanilla.com/
Vanilla is an open-source free forum software solution, standards-compliant, multi-lingual, fully extensible discussion forum for the web made for people running MySQL 3.23 or PHP 4.1 or greater. This free forum software package has built-in spam control, an autonomous user & role management system, and affords administrators a great deal of flexibility and ease-of-use.
As an administrator you can completely change the layout, style, language, and all application settings through an intuitive and easy to navigate settings tab. You can run advanced searches through discussion topics, comments, and users as well as change the way Vanilla operates using per-user preferences.
Vanilla also has a large library of plug-ins that allows you to change almost any aspect of it that you wish. You can even create your own custom plug-ins to even further expand its capabilities.
- MySQL and PHP Compliant