A PHP bulletin board system originally made by John Percival, similar to the ubb. The board requires PHP and MySQL to exist on your server. History:

vBulletin started as bulletin board written by John Percival to replace his ubb, as ubb was slowing down because of the size of his community. When Infopop announced Opentopic, their hosted community solution, a lot of people were angry at Infopop because they felt they had been mislead into thinking Opentopic was a ubb-like board powered by a mysql server, not one remotely hosted by Infopop. They started looking for a replacement, found John Percival's board, and encouraged him to start selling his bulletin board system to others. Now his product has a huge following and is generally considered the best PHP bulletin board available by many(then again, the fans of phpBB and other boards also consider their board the best available). The two-person Jelsoft company has grown bigger and the first vBulletin 3.0 betas have been released already since then.

You can find vBbulletin at Http://www.vbulletin.com.