Conway's Game of Life—the OG cellular automaton toy—is put in three dimensions by Samuel Levy. You can spin the playfield as it mutates, too! It beat the hell out of my computer on the higher settings, though.
Cells (in this case, cubes) with only 1 or less neighbours die, as if by lonliness.
If 5 cells surround an empty cell, they breed and fill it.
If a cell has 8 or more neighbours, it dies from overcrowding.
Strictly speaking, that means it's not the Game of Life but a more elaborate automaton. The results are rather obscure, visually, to me, in this particular setup. I hope this gets expanded to allow for more experimenting with rules.