I've recently been playing around with the WebRTC (web real-time communication) stack, in particular getUserMedia which grants you access to the webcam and mic in javascript. In particular I've put together an alpha of a motion control library that allows the user to swipe their hand and have the webpage respond. More details can be found on the github page, but it makes more sense just to try the demo:
Demo - works in chrome and firefox nightly (at the time of writing)
The library is currently in its infancy but I'm planning to add auto-calibration and other niceties as time goes on. If it doesn't work for you, please let me know in the comments.