Biome is one of several prototype games written during the design of Spore, that Maxis has made available for download.
From the Spore website:
BIOME is a programmable cellular automata simulator that allows users to develop simple "SimCity-like" grid simulations.
Use of Procedural Content Generation Methods
Biome implements examples of cellular automata which are frequently used in procedural content generation, such as fire propagation. It is an excellent tool with which to experiment with a variety of cellular automata in order to mimic various natural processes.