- Continuous physics.
Continuous physics means that the physics is now independent of the frame rate. This prevents bodies from passing through each other at higher speeds. This feature can potentially make this version slower then previous versions, but it also makes it MUCH more accurate.
- Shape create/destroy.

You can destroy a shape on the parent body easily. You may do this to model a breakable object.

In the past you couldn’t add or remove shapes from a body object that was already in the world object.
- Joints defined in local coordinates.

Box2D requires [joint anchor] points to be specified in local coordinates. This way the joint can be specified even when the current body transforms violate the joint constraint — a common ocurrence when a game is saved and reloaded.

- Moveable center of mass.
This is great because you can now have a hammer that’s center of mass is in the head, not the middle of the handle.
- Sensors.

Some times game logic needs to know when two shapes overlap yet there should be no collision response. This is done by using sensors. A sensor is a shape that detects collision but does not produce a response…

- Contact listener callback.
- Contact filter callback.
These callbacks are essentially events. It is now much easier to do something or other on collisions. Say, cause damage to your spaceship when a meteor strikes it.
- Revised manual.
Sure. Having an up to date manual is a good thing. Currently the manual is only for the C++ version, but all the concepts are the same for the flash version and it will help a lot for understanding the example projects.
- Doxygen documents.
- Eliminated deferred destruction.
This was a feature in previous versions of Box2D that was only needed because there was no contact callbacks. It’s gone now so I’m not going to bother explaining what it was.
- Improved testbed with more examples.
Check it out! It’s really just the example project/code that they give you to learn some of the features.

With this release I will be getting back to making some tutorials on how to use this awesome resource. So, keep checking back to see what’s new and I will hopefully not disappoint you.