Each cell counts how many cells within its Moore neighborhood (including itself) is "on". If that number is odd, the cell turns "on" at the next time step; otherwise it turns "off". A simulation starting with a single "on" cell shows the proliferation of the state over the space in a recursive way, creating a 3D Sierpinski gasket in spacetime. You can also place a small "A" by clicking "place 'A'" button or create your own initial configuration by clicking anywhere in the CA space. The information about the initial pattern won't be lost in this CA, and you will see the same pattern replicate and reappear from time to time as the simulation goes on.