Then.js
The fastest, smallest, fully compatible, full-featured asynchronous module!
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
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.