"Rip-Off is a top-down vector shoot 'em up arcade game released by Cinematronics in 1980. It is the first arcade game to feature cooperative gameplay and to exhibit flocking behavior. The objective of Rip-Off is to prevent computer-controlled enemies from stealing eight canisters set in the center of the screen for as long as possible. One or two players control tank-like vehicles while enemies rush onto the field and attempt to drag the canisters off the edge of the screen. Enemies can be defeated by shooting or colliding with them. The game is over when all the canisters are removed from the playfield." Source: Wikipedia, "Rip-Off," available under the CC-BY-SA License.