I recently reinstalled M.A.M.E. on my PC, and went about adding all of the various Space Invaders clones to my Favorites list. It's truly amazing how many hacks, clones, and bootlegs sprung up on the heels the original. There were close to 100 or so games released betwen 1979 and 1983 that were called "Space (something)" or "(something) Invaders". And of the dozens upon dozens of space shooters that tried to one-up the classic SI - only Galaga came close, IMO. There's just a simplistic elegance that makes it still very fun to play nearly 30 years after the fact.My favorite clone would probably have to be Midway's Space Invaders II - not only could you play with another individual at the same time, you and your partner were on opposite sides of the screen, and could shoot at *each other*. A pretty neat little twist if you ask me.