Neighbor-Dependent Substitution System
This is a simplified setup of the system used in the NKS 2007 Wolfram Science Conference presentation "Morphogenesis of a Cellular Automaton on a 2D Substitution Network". The CA can act on the nodes of the network. Nodes in state 1 will divide, introducing three new nodes with states determined by a simple rule. The rule depends on the three nearest neighbors only.
For more information, see the abstract for "Morphogenesis of a Cellular Automaton on a 2D Substitution Network (NKS|Online)".