It is meant to teach kids about the concept of chaos and double pendulum. It traces out the double pendulum, and implements a notion of one trace diverging from another. This uses a possible unique algorithm I call the "bracelet" algorithm that simulates moving a ring or bracelet along both traces.
This was written to argue for the creation of a PHYSICAL version of this that would use a camera and an LED to do this in physical space at the Montshire Science museum, which has so far not agreed to improve their current pendulum exhibit in this way.
Like all Public Invention projects, this is completely open-source---improve it if you can or suggest something to me. I'll make the wild claim that this is already the best double-pendulum simulation on the net (for this specific pedagogical purpose). But I doubt kids enjoy it, so there is much to be