"Meet Vanilla: A New Kind of Web Forum"

"Vanilla - The Sweetest Forum on the Web"...is a free fully extensible solution which comes pre-loaded with extensions, and new ones are added all the time.

"With Vanilla we wanted to break the mold created and followed by just about every other forum on the web. We sat down and thought about what we liked, and more importantly, what we didn't like about web forums. We wanted emphasis on the discussions rather than the statistics. We wanted to stop using MSN or AIM to send secret messages to other forum members; We wanted to be able to save the common searches. Basically, we wanted the thing to work for us instead of against us. Most importantly we wanted it to be free and we wanted it to run on just about every web server out there. So, Vanilla is a PHP / MySQL solution that is 100% open-source. You can take it and alter it and use it free of charge." - Lussumo.com

Vanilla is extremely easy to install, easy to set up, and easy to extend. It features discussion, category, user, and role management. Database backups are a easy and simple.
You can style it any way you want using CSS. Vanilla is is clean and smooth and it's not cluttered with links and buttons you don't understand.

Click Here to Get Vanilla
or
Visit the Lussumo Community to see Vanilla in action