Just so you know, UrbanTerror isn't open-source, sadly - still very good fun though.
There's a pretty fun FOSS FPS called AssaultCube which I used to play a lot - it's simple but it's fun. That has quite a high number of players. Unsure about how active the other FPSs are but whenever I've tried them out I've always been able to get a game.
There's a pretty fun FOSS FPS called AssaultCube which I used to play a lot - it's simple but it's fun. That has quite a high number of players. Unsure about how active the other FPSs are but whenever I've tried them out I've always been able to get a game.