Auto-rig, retargeting, and animation middleware.

AccuRIG. Free application designed for fast and easy character rigging.
APEX (Houdini) Paid. SideFX's procedural node-based rigging framework.
Auto-Rig Pro (Blender) Paid. Automatic rigging and retargeting.
CvWrap. Fast Maya wrap deformer.
EasyMocap. Open-source toolbox for markerless human motion capture and novel view synthesis from RGB videos.
Mesh2Motion. FREE & open-source web application to animate your 3D models. Supports humanoid, four-legged, and bird creatures.
Onion Skin Renderer. Onion Skin Renderer for Maya.
ossos. A complete character skinning & animation library for the web
trigger. Operational code-driven rigging tool for Autodesk Maya.