Sauerbraten/Cube 2

[Dr. Funk]

Sauerbraten A.K.A. Cube 2 is a free to download FPS game with plenty of cool features. It comes with an array of preset maps, cool and creative weapons, free online play with multiple game modes, and an easy and dynamic map editor. The graphics are pretty good too :thumb: .

Their website includes game screenshots, a video, and info about the game's engine.
Sauerbraten Website

 

[Berserker]

I remember cube 1 from school, that was fun.
I might give this a go.

 

[Zethus]

i've played this for a long time... i like doing some spheres lol

 

[DeM0nFiRe]

Another thing worth mentioning is that it is open source under the ZLib license, meaning you can use the engine to make your own games as well.

I have tried out this a few times, it is pretty fun but it's also rather low-tech in comparison to today's engines. It's certainly a fun game to mess around with but it's a bit outdated.

EDIT: Well, don't take my word on that quite yet. I just remembered that when I used this engine I had to dial everything way back. I've got a new gpu now so I'll actually check it out again and report later.