Bacteria

In 'Bacteria' you have a square game field that is in some form of a stable state. You need to add in a certain number of cells so that, after a few steps, the field will be halted (in colored mode) or even cleared (in "hard" black & white mode). You could draw in single points, or use standard 'Life' patterns like "Gliders" (they move at an angle) and "Lightweight spaceships (LWSS)" (they move in a straight line).

Depending on the difficulty level, the player can use a smaller area to add new cells.