Viva La Evolution! An Evolution Simulator by scikidus
Basically: 25% of the creatures who stand out the most against the background are eaten by predators. 25% of the creatures are unlucky and die. The remaining population mates randomly. Each offspring inherits "traits" (a.k.a. the red, green, and blue components of their color codes) from either parent, along with a 50% chance of a mutation. (You can set the mutation level.)
NEW! Set the population size, and download the .fla!