Google Code, one of now approximately a million different websites which start with the word Google, is a sharing platform for developers to exchange open-source programs and nifty things they have made.
One such nifty thing is this Reaction-Diffusion package, based on our old friend Alan Turing’s famous equation. The reaction-diffusion equation, originally given in Turing’s 1952 paper The Chemical Basis of Morphogenesis, provides a model for how a mixture of chemicals, reacting with each other while moving under the action of diffusion, might result in the kind of patterns we see in animal print and elsewhere in nature.
The Google Code Reaction-diffusion page allows you to download some OpenCL based code to run your own simulations of reaction-diffusion systems, as well as some nice videos of patterns resulting from certain initial conditions. There’s also a link to a blog post by the author of the package, which explains how some of the patterns crop up in nature.