I like those ideas!
Here's another to put in the hat:
Survival of the Fittest
Create a simple eco-system with at least 3 kinds of life - plants, prey and predators.
When the program runs, predators chase prey, prey seeks plants and flees from predators and plants spread gradually.
Each life form has a finite life span, but this can vary among individuals among with other aspects such as their speed, etc.
Maybe I've overcomplicated my explanation.