There are many free open source forum system (bulletin board, message board) written in PHP, ASP.NET and Perl. Below is a list of my favor free open source forum collections. I only listed out those forum which has detail documentation, good community support.

P.S This list is not in any particular order

1. phpBB

phpbb

Website : http://www.phpbb.com
Language : PHP
Database : MySQL, Microsoft SQL, PostgreSQL, Oracle, Firebird, SQLite
License : GNU General Public License (GPL)
Version : 3.0.5

This is the most widely used Open Source forum. Credit to it’s huge community support, ton of plugins and mods customization feature. There a a fully Modded phpBB forum as well.

2. MyBB

mybb

Website : http://www.mybboard.net
Language : PHP
Database : MySQL, PostgreSQL, SQLite
License : GNU General Public License (GPL)
Version : 1.4.9

AJAX, features-rich and few plugins and theme available to enhance the existing functionality of your own board.

3. Simple Machine Forum (SMF)

SMF

Website : http://www.simplemachines.org
Language : PHP
Database : MySQL
License : Simple Machines Forum License (SMFL)
Version : 1.1.10 (2.0 coming soon)

Good community support, load with rich forum features.

4. Vanilla

vanilla

Website : http://www.vanillaforums.org
Language : PHP
Database : MySQL
License : GNU General Public License (GPL)
Version : 1.1.9

A bit lightweight if compare with others, Over 400 plugins available in market, theme-able forum.

5. FluxBB

FluxBB

Website : http://www.fluxbb.org
Language : PHP
Database : MySQL, PostgreSQL, SQLite
License : GNU General Public License (GPL)
Version : 1.2

It’s designed to be fast, light and user friendly forum.

6. Phorum

phorum

Website : http://www.phorum.org
Language : PHP
Database : MySQL
License : Phorum License, a BSD Style License
Version : 5.2

High Performance is the key feature, it has flexible hook & module system and good community support. MySQL.com is using Phorum as their forum platform.

7. YetAnotherForum

YAF

Website : http://www.yetanotherforum.net
Language : ASP.NET (written in C#)
Database : Microsoft SQL Server
License : GNU General Public License (GPL)
Version : 1.9.3

The is the only .NET open source forum i heard about, has all the forum neccessary features. However, it’s just hard to find a free or cheap .NET hosting to host this forum.

8. YaBB

YABB

Website : http://www.yabbforum.com
Language : Perl
Database : Flat file based, no database required
License : YaBB Public License (YPL), which is a slightly modified form of the GPL
Version : 2.4

YABB has a long history, develope since year 2000! A forum written in Perl, many features and performance improved since v2.0. Try it if you are familiar with Perl.

9. bbPress

bbpress

Website : http://www.bbpress.org
Language : PHP
Database : MySQL
License : GNU General Public License (GPL)
Version : 1.0

Simple, fast and elegant are the key features. It’s look a bit like Wordpress, and can integrate with Wordpress platform. It’s good choice for bloggers who want to integrate the forum and blog platform together.

10. PunBB

punbb

Website : http://punbb.informer.com
Language : PHP
Database : MySQL
License : GNU General Public License (GPL)
Version : 1.3.4

It has fewer features than many other discussion boards, but is generally faster and lightweight forum.

P.S Please comment below if you have other free open source forum in your collection. :)