Webcam Data (Colors & Humans) Tracking In Real-Time: Tracking.js
It has a very easy-to-use API with few methods and events (which is more than enough).
This opens so many doors in developing stuff that reacts to movements and colors like drawing in a web app with gestures, playing games with a specific-colored controller, etc.
I suggest you watch the demo video provided to see the power of the library, it is really exciting.
Compatibility: All Major Browsers