Scorched 3D: simple (to start, but you'll have to learn to approximate mentally ballistics calculations, taking account of the lie of the land and direction and strenght of the win too) and addictive.
It's a totally free improved 3D version of the old 2D shareware Scorched Earth.
It's multiplatform too, you can run it on Linux, Windows, OSX, *BSD, Solaris and every Posix compliant OS.
http://sourceforge.net/projects/scorched3d/







