AEF - Advanced Electron Forum is a free bulletin board software written in PHP and MySQL with loads of features

The most widely used Open Source forum solution

XMB is a lightweight PHP forum software with all the features you need to support a growing community

Its the easy to use, multilingual, powerful, feature packed, free forum software

The Original PHP and MySQL Forum Software

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

SMF is a free, professional grade software package that allows you to set up your own online community

UseBB is a light and Open Source forum software

FluxBB is a free open source forum application designed to be fast, light and user friendly