Grapnel.js
A simple, lightweight library making it easy to create routes or run events based on a specific URL hashtag.
Boiler
Boiler is a utility library that makes every day tasks in JavaScript easier by providing over 115 methods that work on arrays, collections, functions, numbers, objects, and strings.
Machina.js
js ex machina - finite state machines in JavaScript
Stampit
Create objects from reusable, composable behaviors.
Bacon.js
FRP (functional reactive programming) library for Javascript
Lunr.js
A bit like Solr, but much smaller and not as bright
Fast.js
Faster user-land reimplementations for several common builtin native JavaScript functions.
Backbone.stickit
Backbone data binding, model binding plugin. The real logic-less templates.
Lucid Js
LucidJS is a chainable event emitter library. It offers several unique features such as set events, emitter piping, DOM node encapsulation, sub events, along with the usual event triggering and binding. LucidJS emitters also feature meta events that allow listening for event binding and event triggering. LucidJS works in both the browser and node.js.
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.
Conditioner
Frizz Free, Environment-aware, JavaScript Modules
JS Signals
Custom Event/Messaging system for JavaScript inspired by AS3-Signals
Humane.js
A simple, modern, browser notification system
PreloadJS
PreloadJS makes preloading assets & getting aggregate progress events easier in JavaScript. It uses XHR2 when available, and falls back to tag-based loading when not.
Is.js
Micro check library
Rx Js
The Reactive Extensions for JavaScript
Pilot
Pilot — multifunction JavaScript router.