A free addon to automaticly do physicly plausible animation on arbitrary armatures?

Does anyone know of a free addon (or somthing of the sort) where after i define things like keyframes, the mass of the bones, strength and position of the muscles etc, it will automaticly animate the armature taking in consideration things like inertia versus muscle strength, balance contraints, energy efficiency etc while trying to get the closest to the specified keyframes as physicly possible in the allotted time?

Basicly i’m looking for somthing that will let me animate characters in a physicly plausible way without having to have the skills necessary to hand animate the physics. Sorta making the work of animating characters more like directing (or perhaps choreographing) than animating.

I would like to know of something like this as well.