**Lattice geometry:**1-d, 2-d square or hexagonal, 3-d.**Neighborhood:**square (Moore) neighborhood of radius or nearest neighbors only.**Boundary conditions:**periodic or reflective.**Initial conditions:**problem dependent.**State set:**problem dependent.**Transition rules:**probabilistic, symmetric, often outer totalistic.**Reversible models:**block-CA and partitioned CA.

We have demonstrated the choices using the simple example of the Greenberg-Hastings cellular automaton, which we have extended in many different directions.