I made this program using Flash about 10 years ago just for fun. It was based on an old “recreational computing” Scientific American article by A.K. Dewdney. You can find more elaborate versions of Wator elsewhere, for example here. I tried to make my version focusing more on aesthetics than on customizability.
The basic idea behind Wator is that the brown dots represent “sharks” and the blue dots represent “fish”. Sharks survive by eating fish and fish survive by breeding and not getting eaten by sharks. From these very simple rules you can see what looks like the ebb and flow of real population changes.
It is quite easy for the sharks to eat all the fish and then themselves all die out since they have no more food (insert your own lesson about future of the human race etc here). Whether and how long the shark & fish populations survive depends on the parameters you set such as shark breeding time, fish breeding time etc. In the case of my program I “cheated” by adding an “I am Legend” rule that when there is only 1 shark left, that shark can’t die (ok-can’t remember if that’s actually consistent with I am Legend). If you watch the flash movie for a while you’ll see this happen occasionally.