Underscore
JavaScript's utility _ belt
Knockout Projections
Knockout.js observable arrays get smarter
Davis.js
RESTful degradable JavaScript routing using pushState
JayData
JayData is a unified data access library for JavaScript to CRUD data from different sources like WebSQL/SQLite, IndexedDB, MongoDb, ASP.NET WebAPI, OData, HTML5 localStorage, Facebook or YQL. The library can be integrated with KendoUI, Knockout.js, Handlebars.js or Sencha Touch 2 and can be used on Node.js as well.
Modules Webmake
Bundle CommonJS/Node.js modules for web browser
Flow Js
Javascript Library for Multi-step Asynchronous Logic
Fast.js
Faster user-land reimplementations for several common builtin native JavaScript functions.
Pegasus
Load data while still loading other scripts and display data faster in jQuery, Backbone, Angular, ... apps
Bootstrap Ajax
A library for adding declarative ajax functionality to your website
Backbone Deep Model
Improved support for models with nested attributes.
Sentry
Sentry is a realtime error logging and aggregation platform
Platform.js
A platform detection library that works on nearly all JavaScript platforms.
Amplify
AmplifyJS is a set of components for data management and application communication.
ifvisible.js
Checks if the current page is visible or not
Routie
a tiny javascript hash router
Refluxjs
A simple library for uni-directional dataflow application architecture inspired by ReactJS Flux
Onfire.js
onfire.js is a simple events dispatcher subscribe / publish library (< 1kb). async, simple and usefull.