History.js
History.js gracefully supports the HTML5 History/State APIs (pushState, replaceState, onPopState) in all browsers. Including continued support for data, titles, replaceState. Supports jQuery, MooTools and Prototype. For HTML5 browsers this means that you can modify the URL directly, without needing to use hashes anymore. For HTML4 browsers it will revert back to using the old onhashchange functionality.
Node Browserify
browser-side require() the node.js way
Flux
Application Architecture for Building User Interfaces
Node Decorators
node-decorators
Mediator.js
An implementation of the mediator pattern for asynchronous events in Javascript
Layzr.js
A small, fast, modern, and dependency-free library for lazy loading.
Montage
Core framework: Montage simplifies the development of rich HTML5 applications by providing modular components, real-time two-way data binding, CommonJS dependency management, and many more conveniences. Join us on irc.freenode.net#montage or https://groups.google.com/d/forum/montagejs
Alertify.js
JavaScript Alert/Notification System
Qooxdoo
A Universal JavaScript Framework
Csso
CSS-optimizer
Famous
Famo.us is a powerful JavaScript framework designed to build rich, interactive web applications. It is the only framework that provides an open source 3D layout engine fully integrated with a 3D physics-based animation engine that can render to DOM, Canvas, or WebGL. Famo.us is currently in public beta.
Postal.js
JavaScript pub/sub library supporting some advanced subscription features, plus message capture and replay
Winjs
WinJS project by Microsoft Open Technologies
Is.js
Micro check library
Backbone React Component
A bit of nifty glue that automatically plugs your Backbone models and collections into your React components, on the browser and server
Foundation
The most advanced responsive front-end framework in the world. Quickly create prototypes and production code for sites and apps that work on any kind of device.