Übergame 1.0.4.0

Übergame is a free realistic multiplayer FPS. It's sort of like a sandbox for games of this type, combining many different modes of gameplay with a wealth of maps and content, including an editor. It's also easy to mod, has loads of content and some nice, modern visuals. Latest version is 1.0.4.0, and among many other things it contains a paintball mode, complete with matching weapons. Have a look at the video on the above page to get an idea of it.

Complete with a set of barrels. I'm guessing the red one will explode if shot... :)