phpBB

phpBB is a high powered, fully scalable, and highly customizable Open Source bulletin board package. phpBB has a user-friendly interface, simple and straightforward administration panel, and helpful FAQ. Based on the powerful PHP server language and your choice of MySQL, MS-SQL, PostgreSQL or Access/ODBC database servers, phpBB is the ideal free community solution for all web sites.

Homepage: http://www.phpbb.com/
Disk Space: 2.5 MB
Documentation: http://www.phpbb.com/support/
Support Forum: http://www.phpbb.com/phpBB/
License: GPL