Can you recommend a good physics engine which is easily portable between WebGL and other OpenGL ES implementations like in Android and iPhone?
I don't want a game engine. Only the physics part.
For handheld devices the best option is to use a C/C++ physics API as processing power is quite limited.
There are other option. But these are the most popular and work well on mobile devices.
This probably has an answer somewhere, but if you want a good 2D portable physics engine Box2D is sort of the standard: http://box2d.org/
For 3D, there is probably a huge list somewhere, bullet being fairly popular: http://bulletphysics.org/wordpress/