http://www.conquest-game.com/Pretty nifty turn based strategy game. Its very quick, maybe 20-30 minutes for a game. Its aimed at multiplayer, but I played a few battles against the AI and had a good time, htough I get getting my ass kicked, until I figured things out.
Very pretty, very fun, and only 10 bucks
They have a free demo too.
Turn based games aren't too common these days, so figured I'd pass this one along to you guys.
It runs on linux, mac (not sure if ppc or intel) and windows.
