Box2D 2.4.0 Release was announced for general availability and can now be downloaded and used for prooduction purposes.
Box2D is a free and open-source, cross-platform 2D physics engine for games written in C++. it supports collisions, physics simulations such as contact, friction, restitution, forces, momentum, and so much more.
This new version of the 2D library comes with bug fixes, improvements, and new features.
Some of the highlights in this release include Joint limits that are now predictive and not stateful. There is now experimental 2D cloth (rope), better support for running multiple worlds, all joints with spring-dampers now use stiffness and damping, and added utility functions to convert frequency and damping ratio to stiffness and damping.