Galaga was an arcade game released by Midway in 1981 and was the sequel to Galaxian. I always thought it was a little strange that there seemed to be so few home ports of this game. Despite being one of the most popular arcade games of all time, the first home port was not released in the U.S. until the Atari 7800 version came along six years later in 1987 (though to be fair, it was originally scheduled to be released in 1984).
Galaga could be described as a more sophisticated version of Space Invaders. Like Space Invaders, you control a ship that can move along the bottom of the screen and shoot at aliens firing at you from above. However, there are several types of aliens in Galaga and they attack by swooping down at you in formation. In addition to destroying your ship, they can also capture it. In this case, you have the chance to shoot that alien with a remaining ship (if you have any) and then your ship will return and connect to your current ship for double the firepower.
Much later on, starting in 1995 and continuing today, it has been re-released on a wide variety of systems as online downloads and as part of various compilations but there were not many choices back in the day. It seems like good conversions could have been done on the Commodore 64, Atari 8-bit and Atari 5200.
I did play black and white knock-off called Galagar (I think) on my Commodore 64. It played pretty well but was also pretty ugly.
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