In the "Generations" cellular automata, a cell can have these values: off (0), on (1), or dying (2 or more). The number of generations is the total number of cell states. For example, "Meteor Guns" has eight possible colors or generational states. At each step, the eight cells neighboring each cell are evaluated for the total number of cells that are on, giving some value 0 to 8.
1. Any off cell that touches a "birth" value of on cells will become an on cell.
2. Any on cell that touches a "survival" value of on cells will continue to stay on, otherwise it becomes a dying cell.
3. Any dying cell increments to the next value. Cells matching the generation count turn into off cells.
Some rules, such as Brian's Brain, are well studied.