Modernizr
Modernizr is a JavaScript library that detects HTML5 and CSS3 features in the user’s browser.
Webshim
Webshims Lib is a modular capability-based polyfill-loading library
Lmd
LMD: Lazy Module Declaration. Be lazy: lazy load @ lazy init
Angular History
A history service for AngularJS. Undo/redo, that sort of thing. Has nothing to do with the "back" button, unless you want it to.
Hamsters.js
100% Vanilla Javascript Multithreading & Parallel Execution Library
Radio
Dependency-free Chainable Publish/Subscribe Library for Javascript
Sift.js
filter arrays using mongodb queries
Backbone.stickit
Backbone data binding, model binding plugin. The real logic-less templates.
Platform.js
A platform detection library that works on nearly all JavaScript platforms.
Stately.js
Stately.js is a JavaScript based finite-state machine (FSM) engine for Node.js and the browser.
Fluxible
A pluggable container for isomorphic flux applications
Fetchival
window.fetch wrapper for writing simple and expressive requests
Stampit
Create objects from reusable, composable behaviors.
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.
Invisible
Invisible.js: Reusable models for the client and the server
Mediator.js
An implementation of the mediator pattern for asynchronous events in Javascript
Superagent
Ajax with less suck - (and node.js HTTP client to match)