OpenSim is a freely available software system that allows you to build, exchange, and analyze musuloskeletal models and dynamic simulations of movement.
OpenSim 2.4 includes faster and more robust tools for Inverse Dynamics and Inverse Kinematics, new visualization tools, enhanced access for API users, and several usability improvements. In addition, we’ve verified that the results of Computed Muscle Control now match or exceed the quality of those achieved in OpenSim version 1.9.1. We've added documentation of Induced Acceleration Analysis, application of external loads and several examples. Please see the release notes for more details.
Notes
Seems it contains an API/library part. Maybe it could be used on MH models for animation?