Warzone 2100 is a startegy game that developed by Pumpkin Studios (Archived website) and this game published by Eidos-Interactive , this game offers campaign mode, multi player and also you can try single-player skirmish mode. This game offers ech tree with over 400 different technologies, combined with the unit design system, allows for a wide variety of possible units and tactics.
~1 GHz CPU
64 MB graphics card with good OpenGL support (make sure you have the newest drivers installed)
~100 MB free RAM for the game
~100 MB HD space for the game, up to ~ 600 MB extra for the large videos