Non-human simulations, like mice, worms, flies, yeast, might also qualify if they can be adapted to humans.
It is an adapted version of the Logo language, but greatly enhanced for mathematical visualization. It's a bit Lispy (without all the parens), so the language is pretty much instantly understandable, even if you've never coded before. The download includes both a 2D (very quick) and 3D (slower, but quite amazing) versions. And it is free, since it was written purely for educational purposes.
Most of the examples are very high level (eg: flocking algorithms) or very low level (chemical interactions at the molecular level). You'll probably enjoy the RNA/DNA simulations, and the very detailed simulations of cellular functions such as reproduction and protein synthesis.