ExpressJS - Sinatra inspired web development framework for node.js -- insanely fast, flexible, and simple
Pixi.js - Fast lightweight 2D library that works across all devices
Backbone.js - Give your JS App some Backbone with Models, Views, Collections, and Events
Snap.svg - Snap.svg is a javascript SVG library for the modern web.
FeathersJS - Wow your users. Build incredible real-time applications in record time.
Raphael - Raphael.js is an Object Oriented drawing library. It is good at making in-depth diagrams with complex interactions.