Has around 200 active players and 500 games almost every day. While that might not be much outside the realm of aFPS, it's more than some games that have been given room in this site. It has everything necessary to qualify as a competitive AFPS and it's always a nice alternative for Linux geeks.

Forum: http://forums.xonotic.org/
Website: http://xonotic.org/
IRC Quakenet: #xonotic.pickup