Page.js
Micro client-side router inspired by the Express router (~1200 bytes)
Sea.js
A Module Loader for the Web
Is.js
Micro check library
Batman
Fighting Crime and Kicking Apps
Jquery Timeago
Timeago is a jQuery plugin that makes it easy to support automatically updating fuzzy timestamps (e.g. "4 minutes ago").
Radio
Dependency-free Chainable Publish/Subscribe Library for Javascript
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.
Fluxible
A pluggable container for isomorphic flux applications
Lazysizes
High performance and SEO friendly lazy loader for images (responsive and normal), iframes and more, that detects any visibility changes triggered through user interaction, CSS or JavaScript without configuration.
Vis
Dynamic, browser-based visualization library
Rivets
Declarative data binding facility
Csso
CSS-optimizer
Node Decorators
node-decorators
Nanobar
Very lightweight progress bars. No jQuery
Supermodel
Supermodel - Minimal Model Tracking for Backbonejs
Flight
A lightweight, component-based JavaScript framework
Winjs
WinJS project by Microsoft Open Technologies