2D physics sandbox and (even) in javascript

PHUN is a terrific (FREE!) 2D physics simulator. Totally visual and
very simple to use. Can even be used to make mock-up videogames, since
objects can be controlled by keyboard.

- PHUN
- cool PHUN projects (videos on youtube)
- a binary adder video (a remake of digicomp II)

Some javascript benchmarks also simulate 2D physics:
- here and here
- how to implement 2D physics in javascript and canvas (here)