2D Physics Engines

Box2DFlash
Box2DFlash (ported from C++ Box2D) is a more complete engine with great physics, but maybe has a steeper learning curve because its structure is a little different to what we usually see in AS3.
Supports :

• Advanced constraints
• Circles
• Polygons
• …

APEngine
APEngine is a simple physics engine.
Supports :

• CircleParticles
• RectangleParticles
• WheelParticles
• SpringContraints
• Grouping
• Collision

3D Physics Engines

JigLibFlash
JigLibFlash (ported from C++ Jiglib) is in early development, and is growing really fast.
Supports :

• Papervision3D, Away3D, Sandy3D with built-in classes
• Spheres
• Boxes
• Infinite Planes
• …

Tutorial of JigLibFlash with Papervision 3D

WOW Engine
Supports :

• Spheres
• Infinite Planes
• boundArea
• advanced constraints
• verlet box
• …