Forum Engines (Free Software)
Advanced Electron Forum - Easy to use PHP forum engine.
aterr - Simple multi-threaded board engine.
bbPress - From the creators of Wordpress and Akismet comes an elegant bulletin board.
Beast - A Rails-based forum written in only 500 lines of code.
Beehive Forum - PHP forum engine with support for mobile browsers.
Blursoft MetaForum - Has a ton of AJAX features, but manages to stay search engine friendly. And yes, the back button does work.
bttlxeForum - Basic ASP board.
Deluxe Portal - All-in-one portal solution.
DeluxeBB - Speedy engine with database optimization and GZIP compression.
dnfBB - 3-tier C# forum that works with Firebird and MySQL.
E-Blah - Basic BBS with Akismet spam protection.
Elite Bulletin Board - Light and customizable board.
eXtreme Message Board (XMB) - On the outside, it appears to be a basic forum engine. Until you download the mods for it.
IceBB - Beautiful board with feeds, calendars, and much more.
Ikonboard - Popular forum software. Unique in that it can use both a database or a flat file as a backend.
JForum - Great board with karma, phpBB migration, and search-friendly URLs.
MegaBBS - Fully featured ASP board engine. Note: only free for personal use.
miniBB - Minimalistic board powered by PHP.
mvnForum - Powerful JSP board under the GPL.
mwForum - Great Perl forum with a wonderful look.
MyBB - Plugins and an easy-to-use admin system make MyBB a keeper.
MyTopix - Great forum with a unique design.
nextBBS - Popular board with a ton of features and integration with Mediawiki, Coppermine, and Zoints.
Orca - Nice forum engine with tools like a live post tracker and a WYSIWYG editor.
OvBB - Lightweight vBulletin clone.
Phorum - Popular forum engine that powers boards like the MySQL forum.
phpBB - The granddaddy of Internet forums, phpBB sports a modular design for the control panels, support for almost any kind of database, and a host of plugins. No wonder it won the SourceForge Community Choice Awards' Best Project for Communications.
Pocoo - Never heard of a Python-powered board? Neither did I, until I found Pocoo. It's WSGI compatible, and has an advanced plugin system.
PunBB - With XHTML-compliant pages, simplicity, and speed, what's not to like?
Quicksilver Forums (QSF) - Based on the now dead MercuryBoard, QSF has grown into a mature engine sporting features such as 3D permissions or skinning.
RForum - Strong forum with mailing list integration, powered by Ruby.
Simple Machines Forum (SMF) - Originally a fork of YaBB SE, SMF features WYSIWYG, powerful groups, and much more. Note: there is some dispute about whether SMF is free software or not, since you are not allowed to redistribute the forum/software itself without written permission.
Snitz - Basic ASP forum.
txtForum - Tiny forum that stores its information in TXT files instead of a database.
Unclassified NewsBoard Forum (UNB) - Easy to use forum engine with Jabber notification.
UseBB - Lightweight, clear, and efficient board package.
Vanilla - Terrific AJAXified forum with a really nice look you won't find anywhere else.
Vikingboard - Minimalistic board engine for high performance.
Viscacha - Board with integrated CMS and conversion from CuteCast, Vision Board, phpBB, and WBB.
YaBB - Easy to install and easy to use, YaBB is more than yet another bulletin board.
Yazd - Basic forum engine under the Apache license.
Forum Engines (Commercial)
AspNetForum - Clean and powerful ASP.NET forum engine. $85-$169.
Burning Board - Easy to set up board that will import existing Invision Power Board, MyBB, phpBB, PunBB, Simple Machines Forum, or vBulletin forums. $139.99-$269.99.
FuseTalk - Powerful forum software used by big-names such as Adobe, Boeing, NASA, NBC, US Airforce, McAfee and Lonely Planet. But the names will cost you. $649-$4599.
FusionBB - Calendar, photo gallery, PayPal, article templates, and much more are available with this great piece of software. $425 flat fee or $149 flat fee and $39/year.
Ideal BB - ASP/COM board with a nice revision feature. $299-$2099.
Invision Power Board (IPB) - One of the most popular commercial boards of all time. $149.99-$299.99.
Jive Forums - Powerful board used by companies such as EA and ESPN. Unfortunately, very expensive. $14950 flat fee, $1950/1000 users, $4950/5000 users, or $9950/20000 users.
MyProBB - Powerful anti-spam features makes this one a keeper. It's cheap, too. $25/year.
UBB.threads - $725 flat fee or $229 flat fee and $125/year.
vBulletin - Extremely popular board with tons of features. $160 flat fee or $85/year.
WowBB - WYSIWYG, internationalization, and much more available with this PHP board. $99 flat fee or $55/year.
Blursoft MetaForum - Has a ton of AJAX features, but manages to stay search friendly. And yes, the back button does work. Free.
CuteCast - Basic forum hosting. Free.
GoBoardz - Nice forum with photo sharing and a nice interface. Free.
Hyperboards - A big hosting provider with global login (one Hyperboards account logs you into every Hyperboards forum), skins, pages, and unlimited posts and boards. Free.
Invision Power Board (IPB) - One of the most popular commercial boards of all time. $10-$75/month.
ProBoards - A well known host powered by YaBB. Free.
Sudden Launch - Forum host with unlimited posts, replies, and boards. Free.
WowBB - WYSIWYG, internationalization, and much more available with this PHP board. $99 flat fee and $3.95/month or $7.95/month.
bbPress and Wordpress integration - Official howto on integrating the two sister projects.
FireBoard - Joomla component that adds a powerful forum.
Integrating Vanilla and Wordpress - Official guide to integrating the two popular CMSs.
IpbWiki - Connects Invision Power Boards and MediaWiki.
Joomla!Vanilla - Bridge between the Joomla CMS and Vanilla.
BBCodeXtra Firefox Extension - Context menu to insert BBCode or (X)HTML. Freeware.
HTML To BB Code Converter - Basic HTML or website>BBCode converter. Open source.
Text Formatting Toolbar Firefox Extension - Formatting toolbar for BBCode, HTML, or Wiki code. Freeware. (via)