Zepto.js : Zepto is a minimalist JavaScript library for modern browsers with a largely jQuery-compatible API. If you use jQuery, you already know how to use Zept...
Parsley.js : Javascript forms validation.
Powerful, UX aware & Dead simple.
ClippyJS : Add Clippy or his friends to any website for instant nostalgia.
stream.js : stream.js is a tiny stand-alone Javascript library that unlocks a new data structure for you: streams.
impress.js : It's a presentation framework based on the power of CSS3 transforms and transitions in modern browsers and inspired by the idea behind prezi.com
A library to generate PDFs in client-side JavaScript.