bbpress is a full featured forum package written in PHP/MySQL and features all of the customization love that we’d expect from the folks that brought us WordPress.
Matt Craven is the former editor & publisher of The Blog Herald. Currently, Matt is the co-founder of Bryghtpath LLC, a consulting practice located in Woodbury, Minnesota. Matt's presently looking for new blogging gigs. Ping him at matt (at) bryghtpath dot com. You can follow him on Twitter.