In Evolution, an online Flash app, you simulate the principles of evolution (well, some of them). You start out with a screen of a few different amoeba-like creatures, each with their own genetic code and characteristics. You designate food zones and the rate at which food is generated. The creatures each seek out food and move toward it as fast as their genetic code will allow them. When they eat, they reproduce (asexually, no she-bang bang going on, so perverts can go elsewhere).
You can draw lines in the sand that trap the creatures in certain areas of the screen and then just test out different scenarios. What will happen if food is dropped plentifully on one side of the stream and not the other? What happens if you bump up the mutation percentage? Will you get different creatures? And will they be able to survive? This simulation is similar to many other simulations online, but it is fun to play around with and serves as an interesting screen saver as well.