Genr8 has a feature for reading rewrite systems (or grammars) from a file. On this webpage are a few rewrite systems that I have found particularly interesting.
Genr8 can parse probabilistic rewrite systems. Here is an example of one that I think produces some interesting results. It differs very little from the predefined tiles 4 rewrite system.
Edge0 + ~ Edge1 + ~ Edge0 + Edge1 Edge0 -> Edge0 [ [ + + Edge1 ] - - Edge1 ] Edge0 Weight 4 -> Edge0 - Edge0 + + Edge0 - Edge0 Edge1 -> Edge1 [ [ + + Edge0 ] - - Edge0 ] Edge1 Weight 4 -> Edge1 \ Edge1 / / Edge1 \ Edge1 Angle 45
This rewrite system is time-dependent which means that different rules are applied depending on the age of the edge.
Edge0 + ~ Edge1 + ~ Edge0 + Edge1 Edge0_i -> Edge0_i+1 [ [ + Edge1_i ] - Edge1_i ] Edge0_i+1 If i < 3 Edge0_i -> Edge0_i+1 Edge1_i -> Edge1_i+1 [ [ + Edge0_i ] - Edge0_i ] Edge1_i+1 If i < 4 Edge1_i -> Edge1_i+1 Angle 90