Forums and Message Boards
Great tools for open communication on your site. They do take some work though - an un-managed message board will drive people away from your site.
phpBB is used by millions of people on a daily basis, making it the most widely used opensource bulletin board system in the world. Whether you want to stay in touch with a small group of friends or are looking to set up a large multi-category board for a corporate website, phpBB has the features you need built in.
Simple Machines Forum
MyBB is a free bulletin board system software package developed by the MyBB Group. A lot of thought has gone into the MyBB interface to make it easy to use. MyBB uses a standard discussion board structure, so your visitors will feel familiar with the way MyBB works.
Advanced Electron Forum is a free bulletin board software written in PHP and MySQL.It has a lot of unique features and is very fast.Features include UTF-8, SEO URLs, IP Ban, W3C Validated, News System, ShoutBox, Threaded Mode, WYSIWYG, Themes, Languages etc
Vanilla Forums are open-source, standards-compliant, customizable discussion forums
PunBB is a fast and lightweight PHP-powered discussion board. 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.
XMB is a lightweight PHP forum software with all the features you need to support a growing community. With outstanding community support and contribution, you will find XMB to be easy to setup, customize, and enhance.
FluxBB is a free open source forum application designed to be fast, light and user friendly. FluxBB's code, written in PHP, has a proven track record of stability and security. FluxBB is being actively developed.
Phorum was the original PHP and MySQL based Open Source forum software. Phorum's developers pride themselves on creating message board software that is designed to meet different needs of different web sites while not sacrificing performance or features.
bbPress is forum software with a twist from the creators of WordPress. bbPress is plain and simple forum software, plain and simple. It’s easy to use, easy to administrate, fast and clean. But don’t let its simplicity deceive you; underneath the gleam, it’s got some powerful features and is highly customizable
FUDforum (Fast Uncompromising Discussion Forum) is a free and open source web discussion forum. FUDforum combines an extensive feature set while maintaining the ability to generate forum web pages extremely fast. The forum includes i18n and templating support allowing for a complete customization of its output as well as a very capable group based permission system. FUDforum can also act as a Mailing List Manager, USENET newsreader and even an XML Feed Aggregator. This will allow you to build an instant community and consolidate all your messages into a single system.
miniBB is a standalone, open source program for building your own Internet forum. If you want a light, simple and stable message board attached to your existing website at the very high integration level, which may include the full customization of the layout to the look of your website, or even synchronizing with the existing membership system, you've just came across to the best forum solution for such purpose available worldwide.
Beehive is an online forum/message board system with several powerful features. Beehive is an open-source project for creating a high-configurable frame-based discussion forum. Almost every aspect of Beehive is customizable to some degree, from the forum's name right down to how many posts per page each user wants to see and with everything in between, including guest accounts, user profile categories, your start page, your top frame, user's signatures, language packs, forum styles and emoticon sets - and if you don't like those that come as standard, it's easy to create add your own!
my little forum is a simple PHP and MySQL based internet forum that displays the messages in classical threaded view (tree structure).