In Move a Cube With Your Head or Head-Tracking With WebGL, Jerome Etienne talks about 3D head tracking using Three.js and WebRTC. He's using a library for face and head tracking called headtrackr by Audun Mathias Øygard, which has been used to create some interesting demos and games (check out Targets and FaceKat).
Clouseau (GitHub: hull / clouseau, License: MIT, npm: clouseau-js) by Xavier Cambar tracks applications using PhantomJS combined with Q. It basically provides a lightweight integration testing solution:
Once you've defined invariants in your app, you provide Clouseau with functions to assert them. Then Clouseau will open in PhantomJS the URL at which your app resides and will applies these functions.
It can be used for testing, but the author also notes it works for monitoring long-running applications.