Wa-Tor
Wa-Tor is a population dynamics simulation devised by A. K. Dewdney and presented in the December 1984 issue of Scientific American in a five-page article entitled "Computer Recreations: Sharks and fish wage an ecological war on the toroidal planet Wa-Tor". (T)he planet Wa-Tor ... is shaped like a torus, or doughnut, and is entirely covered with water. The two dominant denizens of Wa-Tor are sharks and fish ... Wa-Tor is usually implemented as a two-dimensional grid with three colours, one for fish, one for sharks and one for empty water. If a creature moves past the edge of the grid, it reappears on the opposite side. The sharks are predatory and eat the fish. Both sharks and fish live, move, reproduce and die in Wa-Tor according to the simple rules defined below. From these simple rules, complex emergent behavior can be seen to arise. (Wikipedia).
