My GitHub search skills aren't the best, but here are some of the nicer ones I've found:

Dynamic Physics Interactions for the Mobile Web: https://github.com/luster-io/impulse

Facebook and Path style side menus: https://github.com/jakiestfu/Snap.js/

Smooth scrolling: https://github.com/cubiq/iscroll

Add to home screen call-out for mobile devices: https://github.com/cubiq/add-to-homescreen

Cross-browser usage of the JavaScript Fullscreen API: https://github.com/sindresorhus/screenfull.js/

Anybody know of any more?