An engine where the cells have history. Similar to Life, the number of neighbors affects whether a cell can stay alive, or be born, with the change that history is taken into account.
There are many states, depending on the specific rule in effect. The states have an order, and when in Life a cell would die, here in Generations a cell advances to the next state until it reaches the last state and it dies. If there are sufficient neighbors in the first living state, a cell is born. Again only neighbors 1-8 are considered, but just whether that cell is dead, alive, or in the first living state.