"Jelly" simulates a piece of bouncy and stretchy material in 2D. It breaks under a heavy load - be it compression or stretching. This Jelly below was spinning a little bit too fast:
You can download the program and create a Jelly of any rectangular shape. It lets you tune the strength and stiffness of the bonds, set gravity, load and save your Jelly and tweak a few other settings. Here's an example of a flexible strip, with color indicating the amount of stress:
The Jelly can be manipulated with the mouse. The left mouse button lets you drag it around while the right one spins it. It feels almost like you're touching it with your hands - I can't stop wishing I had a second mouse pointer! (which is actually possible in theory).
If you enjoy the program make sure to learn the keyboard shortcuts - they'll let you set up a jelly much faster and easier.
Update - major breakthrough in stability :)
I have at last persuaded myself to drop the naive approach and use a grown-up integrator for the physics. Turns out (surprise, surprise!) that the Runge-Kutta method makes the Jelly extremely stable. Moreover, it's not even that hard to implement! I really should have tried this earlier.
It will take a while to turn this into a polished release (given current time constraints it's probably many months away), but watch this space...