Free forums
There is plenty of choice when it comes to free forum software. Here is a list of the best.- http://fudforum.org/forum/
FUDforum is a highly customizable forum package, with a large feature set.
- http://getvanilla.com
Vanilla is an open-source, standards-compliant, multi-lingual, fully extensible discussion forum for the web.
- http://www.ikonboard.com
Ikonboard is a comprehensive web bulletin board system.
- http://phorum.org/
Phorum is a little different from the other web based message boards out there. It was designed to meet different needs of different web sites while not sacrificing performance or features.
- http://www.phpbb.com/
Since its creation in 2000, phpBB has become the most widely used Open Source forum solution. Like its predecessors, phpBB 3.0 "Olympus" has an easy to use administration panel and a user friendly installation process, which allows you to have a forum set up in minutes.
- http://www.punbb.org/
PunBB is a fast and lightweight PHP-powered discussion board. It is released under the GNU General Public License. Its primary goals are to be faster, smaller and less graphically intensive as compared to other discussion boards. PunBB has fewer features than many other discussion boards, but is generally faster and outputs smaller, semantically correct XHTML-compliant pages.
- http://www.simplemachines.org/
Simple Machines Forum - SMF in short - is a free, professional grade software package that allows you to set up your own online community within minutes.