phpBB™ (“PHP Bulletin Board”) is the world's leading Open Source forum software. Distributed under the GNU General Public License, phpBB is free software, developed by volunteers from around the world. phpBB is used on over 2.4 million commercial, non-profit, social networking and community websites in over sixty languages. Learn more...

SMF is an advanced community software package that enables you to set up and manage online community forums. Learn more...

Vanilla is a free lightweight and extensible open source forum software using PHP scripting language and MySQL database management system. Learn more...

YetAnotherForum.NET (YAF) is a Open Source discussion forum or bulletin board system for web sites running ASP.NET. The latest version is ASP.NET v2.0 with a Microsoft SQL Server backend. The full C# source code is available licensed as GPL. Learn more...