Davis.js
RESTful degradable JavaScript routing using pushState
Serenade.js
Client side MVC framework
Backbone.stickit
Backbone data binding, model binding plugin. The real logic-less templates.
Aura
A scalable, event-driven JavaScript architecture for developing widget-based applications. Works with Backbone.js and other frameworks.
Dozerjs
Foundational Framework for NodeJS Web Services
ifvisible.js
Checks if the current page is visible or not
Optics
Profunctor implementation of Lenses, Prisms, Traversals, Isos, etc.
Inject
AMD and CJS dependency management in the browser
Ect
Fastest JavaScript template engine with embedded CoffeeScript syntax
Across Tabs
Easy communication between cross-origin browser tabs
Twitterlib
Twitter JavaScript API library
Tweet
put twitter on your website with tweet, an unobtrusive javascript plugin for jquery
Mediator.js
An implementation of the mediator pattern for asynchronous events in Javascript
Bottlejs
A powerful, extensible dependency injection micro container for JavaScript applications
LABjs
Loading And Blocking JavaScript: On-demand parallel loader for JavaScript with execution order dependencies
YUI3
YUI is a free, open source JavaScript and CSS library for building richly interactive web applications.
Theory
Abstraction layer for cross platform JavaScript.