I am on another forum like gaming forum here, but it is also dead. It gets the average post or two everyday or every other day, but that's it. Both forums are inactive as hell.
I tried to revive http://forum.tecmokoei-europe.com/ (whcih is the gaming forum) but it is dead like here.
Facebook and Twitter destroyed most 'smaller' forums, and only large forums live.
Really the only other GTA Forums I can think of is GTAForums, GTAGaming and GTA.ru (russian gaming forum). GTAGaming is semi-active unlike here, which is just well... dead.
But if a forum is about certain subject that is not popular on Facebook/Twitter, those forums kinda 'live'. It's just the social stuff like Gaming, movies, tv shows, sports... etc that get destroyed by Facebook and Twitter.
edit: But whatever if GTAForums get hacked ever, we may see temporary boost in traffic.