Recs.
Updated
Set in a futuristic cartoonish world, Warsow is a completely free fast-paced first-person shooter (FPS) for Windows, Linux and Mac OS X.
Warsow is the Art of Respect and Sportsmanship Over the Web.
SpecsUpdate
Pros
Pro One of the best gateway arena shooters for your friends
Well optimized, small file size, good bots, cute graphics, free, standard arena weapon set, good tutorial... If you are trying to get your friends to try playing hardcore arena shooters with you, like your Quake, UT, Reflex or what have you, this is a quick and free download that won't take too much convincing that will also give you a great experience.
Pro Ultra-fast gameplay
Here some numbers: Warsow is based on Quake game engine, just like Counter-Strike so numbers are comparable. In CS you are moving usually at speed 320 ups. In Warsow average duel match goes with speeds 600-900. In CA mode most of players moving at speeds around 1000ups. And in insta CA mode on some maps you can expect opponent flying at 1500-2000ups.