Simple Machines Forum is an open source solution to creating a full-purpose message board on your self-hosted website.
Simple Machines Forum (better known by the acronym SMF) is seeing some success with developers by taking the complexity out of message board creation. Similar to the more widely known phpBB message board script, Simple Machines Forum's creators claim it is less subject to security threats than other message board scripts in its class.
In fact, there really aren't that many major differences between Simple Machines Forum and others. Simple Machines Forum offers a complete administration panel, with the creation of the forum and subforum (tree system), the ability to create groups, choose a theme and alter the layout to your tastes.
Simple Machines Forum highlights include a very light code, which ultimately makes it much faster than phpBB. Another nice surprise is that it's fairly easy to integrate with content management systems such as Joomla!. The developmental versions of SMF also offer a lot of great add-ons, called mods. Some of these include sub-accounts, a built-in profile chat system and profile status updates. Unfortunately, every time a new release candidate comes out and you update, you're likely to lose the functionality of the mod unless either the mod's creator updates the script or you're willing to tweak the code yourself.
If you're looking for a forum creation tool that is both fast and light, Simple Machines Forum should do the trick.