It's obviously http://www.gaiaonline.com/asyncalerts/

(Lol but in all seriousness, asyncalerts is something you can enable to have popups about your friend's activity on Gaia on any page you're on. So you can be browsing the forums, and if you have asysncalerts enabled a little yellow box will pop up saying "Your friend _______ has just updated their avatar!" or "_______ Has just posted in _________")