[gilleain]

Hmmm. PyMol is molecular viewer, which has a python scripting interface to various libraries ... but is not a folding library I would say.

There is some research into the topology of DNA (especially circular DNA, like plasmids which is a knot) that considers things like writhe and twist. Not sure it would adapt too well to macroscopic systems though.

There is also the excellent KnotPlot for actually drawing the knots. I bought a licence once on a whim, but rarely use it :)