Unvanquished is an open-source FPS game featuring team-based strategy and RTS elements, pitting humans against aliens in a futuristic setting.
https://forums.unvanquished.net/
Tremulous has outdated graphics and almost dead development, yet it still has active games and even gets new players: http://new-edge.org/forum/showthread.php?tid=664
While Unvanquished has active development and good graphics, yet even 3vs3 games are a rarity.
We aren't done yet and have largely spread our playerbase through word of mouth. The community we do have so far is pretty tightly knit. Also, multiple Tremulous servers have expressed an interest in transferring over once we hit beta, so we have that to look forwards to.