...It has ascii-art and nice graphics version, and a special funny version
It's a very basic thing: there are free rigid bodies and springs with strong attenuation/damping. It's very simple and very short code, and collisions of bodies with ground are good and stable.
A good simulation of this kind, however requires Lagrangian method. I proposed the Lagrange_motocross as an alternative of this kind. The code is not much longer but the it's overall more complicated, and collisions are a bad issue.