Xenophobe

Xenophobe is a 1987 arcade game published by Bally Midway. Starbases, moons, ships, and space cities are infested with aliens, and the players have to kill the aliens before each is completely overrun.

This game was unusual in that it split the single monitor into three separate horizontal sections, one for each player. This allowed the players to cooperate, but also allowed the separate players to wander around freely, a feature not found on most cooperative multi-player games. With most games that allowed multiple players at once, all players were bound by the edges of the screen (that is, all the players had to be in the same general area on the screen, so it could contain them all). Because the game featured such high resolution for its time, the split screen didn't detract from the game's graphic appeal.

Source: Wikipedia, "Xenophobe_(video_game)," available under the CC-BY-SA License.