Anyone can download it and play for free. Urban Terror is available for windows, linux and macintosh, the current version is 4.1.
Urban Terror can best be described as a Hollywood tactical shooter; it is realism based to a certain extent (environments/weapons/player models), but also goes by the motto "fun over realism" (fast gameplay and lots of action). This combination of reality and action results in a very unique, enjoyable and addictive game.
Graphics not up there, but it has some nice game mechanics, like you will bleed out if hit too many times, you chose not to wear body armour etc. Powerslide, walljump etc. not bad..
-- http://www.urbanterror.net
Totally Free.. based on Quake 3 engine which means, we can all play it maxed, no cracked servers to worry about.