That's phpBB which I'm running on In4mador and Brad Sucks. It's pretty cool though there are often exploits.
I think what it's doing for the tracking is just saving the time of your last page load and referring to that. In Stripcreator's forums I rely on the cookie, which is why it's tied to the machine you're on rather than the account.
My way's a little less resource intensive for the server, but their way is definitely more convenient for the user. I'm trying to think of a way to tie the new "who's online" system (which tracks pretty much the same data, I think) to a new new post tracking system.
As for the avatars I haven't really played with them much. How do they work?