Hi all. I put together a work in progress demo of a simple physics engine that can handle particles connected by springs. This uses a method known as Verlet integration which is stable and efficient, so you can simulate dozens of springs in real time.
The cart includes 4 demos: a pendulum, a string, a cloth, and a deformable rigid body.

The library implements the approach laid out by Thomas Jakobsen in the article Advanced Character Physics. The syntax is inspired by the physics simulation library toxiclibs.
Here's an example of the syntax to create two particles connected by a rigid spring (i.e. a pendulum).