This program's a slavish imitation of Karl Sims's work on evolutionary art.
It shows you 16 random pictures; you pick which you like best and the program generates 16 random variations on that one, and we keep repeating until you have a cool enough picture or you're just sick of it. Here are some of the better results produced by different runs:
Pictures are generated from programs represented as trees. We first compile the tree program into a C program, then invoke an external C compiler and finally invoke the result. Asking the C compiler to optimize turns out to be a bad idea, at least with gcc: compilation takes so much longer we're a bit better off with unoptimized code. It might be worth trying lcc instead.
Here's the code. It's in Scheme and C.
See also the gallery produced using a descendant of this program.