There are a few of them that are free or opensource for rigging characters and animating them. All of them are free some use propritary file formats.

Blender has just about everything you would need to build, rig, animate, physics, cloth, etc. Best free one out there, huge community support.

K-3D includes basic tools for NURBS, patches, curves and animation.

SoftImage XSI, free version can't be used for comercial work. Used mostly for free games.

Anim8or.

Seamless3d, kind of crude, great for animated toonish stuff.

3D Canvas.

Bishop3D, uses POVray render engine.

Houdini Apprentice, its a trial, never expires, limited render output and water marked, does not support external render engines (full version can use tons of them), not sure what else would be turned off in it. Full version is uber expensive. Houdini is top of the line, steep learning curve as well. Standard desktops will be painfully slow with lots of sims going.

Cant think of anymore, but there probably are some.

There are more than a few that are not free as well. Most of the high end ones will do advanced character rigging for animation and life like poses.

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