AssaultCube

AssaultCube is for those who are prefer rifles to lasers in their FPS games. It takes place in a realistic setting, but still focuses on fast arcade-style matches. It's all about Deathmatch, Survivor, Capture the Flag, etc - tweaked and tuned for minute balance.
One of the most interesting and impressive features of AssaultCube is it's size and system requirements. It runs on pretty much any computer with a 3D card and it's only a meager 40 mb to download. Using an Pentium III with a 56k modem? No problem, you can still play and enjoy AssaultCube. And with 26 maps, 12 game modes and lots of features it has a lot of content for it's small size. Sure, it doesn't look amazing, but it looks clean, has some interesting environments and plays well. Think of it as a minimalist-FPS and you might be happily surprised! Give it a go here!

Simple, yet well made and full of functions,