If you're in the mood to shoot down some aliens, Mac ASCII Invaders plays exactly the way you expect it to: left and right arrows to move your weapon, the space bar to fire. This is Chuck Houpt's Macintosh port of Thomas Munro's ASCII version of Space Invaders.
It's a "termlet"; you install the software into your Applications folder and double-click to run. It then launches Terminal for you and loads up all the backgrounds, font colors and the software you need to run the game. You'll see the Mac ASCII Invaders icon close from your dock and be replaced with the Terminal icon.
Mac ASCII Invaders is SmileWare. Houpt writes: "If it makes you smile, please pass the smile along."