Viggle

Viggle takes the motion out of one video and puts it onto a character you supply, so that animating something no longer requires filming a performer in a capture suit. Its site frames this as 3D character animation without the traditional mocap pipeline, and the feature set follows from there: swap one character, swap several, add motion to a still, control a character in real time, or reach it through an API.

The practical use is the one that used to cost the most: a specific movement — a dance, a gesture, a piece of physical comedy — performed once and applied to a different subject. That is a real shortcut for short-form and social video, which is where the tool is clearly aimed. The two things to be careful about are the same as anywhere in this category: whatever is distinctive about the output comes from a source video somebody else may have rights to, and the technology that swaps a person into someone else's movements has an obvious likeness problem that the tool does not solve for you.