After he saw my post about SimPy, Luis Lafuente pointed me to NetLogo, a very nice cross-platform multi-agent modeling environment. NetLogo comes with a large library of pre-constructed models, coming from the fields of art, biology, chemistry, physics, computer science, earth science, games, mathematics, networks, social science and system dynamics.
Even before downloading NetLogo, you can try out the full library of models in your browser. For example, if you try the wolf-sheep predation model (after starting the model, just hit the “setup” and then “go” buttons to run with the defaults), you’ll see that the sheep population will grow, which will induce the wolf population to grow, and then the wolves will eat all the sheep, leading to a catastrophe for the wolf population. However, if you add grass to the model (switch the grass button from “off” to “on” before hitting “setup” and “go”), you’ll find interesting cyclical dynamics, without catastrophic extinctions (sheep eat grass; then wolves eat sheep; then grass grows again).
Of course, the important point is that in addition to learning about and playing with the existing models, you can easily construct your own, using the NetLogo language.