JForum looks very nice but I'm concerned about the fact that the Git repo used for development has been inactive for over a year now. The last commit for v3 was Feb. 12, 2012:
Yes, Rafael acknowledged at some point that work on JForum 3 was very slow, as he was the only one working on it. Not sure if that's still true now. if you're looking for a somewhat active branch, check out https://code.google.com/p/jforum2/.