Reasondb
A 100% JavaScript object database: SQL like syntax, full-text search, auto object sync, swapable persistence engines, asynchronous cursors, streaming analytics, 18 built-in plus in-line fat arrow predicates, predicate extensibility, indexed computed values, joins, nested matching, statistical sampling and more.
Pdfmake
Client/server side PDF printing in pure JavaScript
Ladda
Buttons with built-in loading indicators.
Jo
Jo is a thin (~12K) candy shell for PhoneGap apps. It's an HTML5 mobile app framework which provides UI widgets, a flexible event model, a wrapper for sound, and a light data layer. Apps are skinnable with CSS3, and work everywhere PhoneGap does... and then some, including Adobe Air and OSX (desktop and dashboard).
Jasmine Ajax
jasmine-ajax - A library for faking Ajax responses in your Jasmine suite.
Hammer.js
A javascript library for multi-touch gestures // You can touch this
Browser Sync
Keep multiple browsers & devices in sync when building websites. http://browsersync.io
Bacon.js
FRP (functional reactive programming) library for Javascript
Almond
A minimal AMD API implementation for use after optimized builds
Aja.js
Ajax without XML : Asynchronous JavaScript and JavaScript/JSON(P)
Smooth State.js
Unobtrusive page transitions with jQuery.
Jquery.payment
A general purpose library for building credit card forms, validating inputs and formatting numbers.
Retina.js
JavaScript and LESS helpers for rendering high-resolution image variants
Processing.js
A port of the Processing visualization language to JavaScript.
Imagesloaded
JavaScript is all like "You images done yet or what?"
Stampit
Create objects from reusable, composable behaviors.
Modernizr
Modernizr is a JavaScript library that detects HTML5 and CSS3 features in the user’s browser.