DMS, the Discrete Models Simulator:

DMS is a program written in Caml, an ML dialect. It is used to simulate the behaviour of a dynamical model described with a set of rules. The output is the graph of all reachable configurations given an initial configuration defined by the user. The structure of the set of reachable configurations often is a lattice but the program will also work on cyclic structures. It is also possible to crop the graph at a certain depth - this is particularly useful in the case of infinite structures. Along with the GraphViz package, it makes it simple to produces images like these.