Free PHP Message Board Scripts

Simple Machines
This is a free forum software package based on PHP and MySQL.

phpBB is a high powered, fully scalable, and highly customisable open-source bulletin board package that supports unlimited boards and posts, instant messaging, multiple languages, searching, private and public forums, and templates. Requires PHP and MySQL, MS-SQL, PostgreSQL or Access/ODBC database server.

Phorum is an open source web based message board written in PHP. The databases the current release supports MySQL and PostgreSQL.

MercuryBoard is a new bulletin board script written in Object-Oriented PHP4, and utilizes a MySQL database.

UseBB is an easy-to-set up and easy-to-use Open Source PHP/MySQL bulletin board system with several user and administration possibilities, especially designed for small to medium sized web sites which do not need the overdose of features found in other forum packages.