what is the forum plug in being used on the wpmu site?

I am a new user and testing multiple installs and plug ins out. I am moving over from a Forum based system (vbulletin) and while I don’t need all the bells and whistles of that forum I wouldn’t mind having something a bit more robust. From what I have seen using buddypress and that also the forum plug in it’s fairly plain. However, on this site it seems to have a bit more going for it. What is being used here and how do I use it on my site?