Leaflet : A Modern, Lightweight Open-Source JavaScript Library for Interactive Maps
Microjs : Fantastic Micro-Frameworks and Micro-Libraries for Fun and Profit!
ClippyJS : Add Clippy or his friends to any website for instant nostalgia.
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...
meSpeak.js : meSpeak.js (modulary enhanced speak.js) is a 100% client-side JavaScript text-to-speech library
A lightweight library that provides tools for organizing asynchronous code