Microwar is a free and open-source 'Space Invaders style' arcade video game developed by Mad Dog Production. Unlike the original Space Invaders game, your ship is replaced with a Macintosh computer and the invading aliens are Windows PC's. The gameplay is quite the same, you control your Mac left to right shooting Windows PC's using your spacebar and trying to dodge their bombs.
Intel or PowerPC powered Mac
Mac OS X 10.4 or newer
Free download at microwar.sourceforge.net