Pegasus
Load data while still loading other scripts and display data faster in jQuery, Backbone, Angular, ... apps
Lazy.js
Like underscore.js, but lazier
Refluxjs
A simple library for uni-directional dataflow application architecture inspired by ReactJS Flux
Invisible
Invisible.js: Reusable models for the client and the server
Mediator.js
An implementation of the mediator pattern for asynchronous events in Javascript
Cellx
Ultra-fast implementation of reactivity for javascript
Pilot
Pilot — multifunction JavaScript router.
Min Pub Sub
198 byte publish/subscribe messaging micro-framework
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.
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.
Backbone.stickit
Backbone data binding, model binding plugin. The real logic-less templates.
UI Router
The de-facto solution to flexible routing with nested views
Use.js
An AMD/RequireJS plugin for consuming incompatible JavaScript files.
Lunr.js
A bit like Solr, but much smaller and not as bright
Bottlejs
A powerful, extensible dependency injection micro container for JavaScript applications
Grapnel.js
A simple, lightweight library making it easy to create routes or run events based on a specific URL hashtag.