MyBB for the win.

I think it's the most powerful forum system that's free.

It's sort of a combination of vBulletin and IPB.

http://www.mybboard.net/

I think I will stick with phpBB, I preferred phpBB2 over phpBB3 but for the sake of security and compatibility, I'll use phpBB3.
The problem now is that I've lost most of my users.

Replying to Laurence

My personal favorite free forum script is phpBB, but you'll need to have mySQL on your server to run it, and if you're not familiar with the database structure of your server, you'll want to have a MySQL administration console... It makes it a lot easier to manage your databases (free as well, but your webhost may charge for that service).

-reply by Typlu

Well i was once a Invision Free man, but then i switched to PHPBB3 and it was great but as I went along and used it, some features weren't the best they could be.

I then tried some other ones and found SMF (Simple Machines Forum) to be the best, loved how simple it was. Also if you get it right it can be really good to look at.

But now I have my own website and my website partner bought vBulletin and it was easily the best, very easy to edit skins with and to control. Heaps and heaps of good extensions.

But as far as a free forum goes i would definitely go SMF.

I'll go into further detail later, but right now SMF, because of the packages system, but there are other reasons.