As with everything I guess, the answer is "it depends".
In particular, are you looking for a bulletin board service (for example
http://www.ezboard.com/ ), a bulletin board application for a particular platform (and which one), or some sort of deployable web-application? Are you concerned about whether you can get the source code? Are you concerned about what systems it will run on ? what languages/librries it uses ?
If you can give us a bit more information about how you plan to use such a system, we can probably come up with some more specific answers.
By the way, I think this topic is more appropriate to "General Computing" than "Java News", so I've moved it for you. Please continue the discussion in the General computing forum. Thanks.