Announcing my port of the Traer v3.0 physics engine to Objective-C/Cocoa: CMTraerPhysics.
Traer Physics is a particle system and spring physics simulator, originally created by Jeffrey Traer Bernstein. It is used to simulate spring and attraction forces between particles, and can be used for some interesting effects.
The CMTraerPhysics source includes a sample iOS app containing a number of physics demos, including a Wonderwall-like demo, a cloth physics demo and a spider web demo. See videos of some of the demos on YouTube.
The demo app is universal so you can play with the physics demos on both iPhone and iPad. The source for all demos is included with the project. Some demos are rendered with OpenGL ES 2.0, some with Core Animation.
The CMTraerPhysics source is available on github at https://github.com/chrismiles/CMTraerPhysics and is released open source under the MIT license.