Vex is a modern dialog library which is highly configurable, easily stylable, and gets out of the way. It's tiny, has a clear and simple API, works on mobile devices, and can be customized to match your style in seconds.
Parallax.js is simple, lightweight Parallax Engine that reacts to the orientation of a smart device. Where no gyroscope or motion detection hardware is available, the position of the cursor is used instead.
tween.js is a super simple, fast and easy to use tweening engine.
Mike's Modal Library is a Facebook like photo library written to support photos and comments on an individual photo.
Echo.js is a simple image lazy loading library, it's less than 1KB minified.
Lazy-loading works by only loading the assets needed when the elements 'would' be in view, which it'll get from the server for you upon request, which is automated by simply changing the image src attribute.