script.aculo.us : script.aculo.us provides you with
easy-to-use, cross-browser user
interface JavaScript libraries to make
your web sites and web applications fly.
Wave.js : Audio visualizer library for javascript. Create dynamic animations that react to an audio file or audio stream.
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...
PeerJS : Peer-to-peer data in the web browser.
PeerJS completes WebRTC as an API abstraction, connection broker, and binary serialization format
stream.js : stream.js is a tiny stand-alone Javascript library that unlocks a new data structure for you: streams.
nlp_compromise does NLP in the browser. It's a handy, and not overly-fancy tool for understanding, changing, and playing with english. We've also got a modest, though ambitious plugin ecosystem.