Building a forum is no small task. The history of bbPress is rich with stories but ever since it became a WordPress plugin instead of a separate install, working with it has been nothing short of fantastic. Not only is it a fantastic plugin to use, but it's (in my opinion) equivalent to a fantastic textbook about writing a WordPress plugin. Fantastic piece of software. With the team behind bbPress I wouldn't waste time looking into anything else to power a forum on my site.