Yahoo User Interface Library (YUI Library):
YUI is a free, open source JavaScript and CSS library for building richly interactive web applications.
Link : http://yuilibrary.com/
EXTJS:
With an advanced MVC architecture, plugin-free charting, and modern UI widgets, Sencha Ext JS is the industry's most powerful desktop application development platform.
Sencha Ext JS provides unparalleled cross-browser compatibility enabling you to develop incredible web apps for any browser.
Sencha is the new name for ExtJS, which has been developed based on YUI, Yahoo! User interface Library
Link : http://www.sencha.com/products/extjs/
jQuery:
jQuery is a fast and concise JavaScript Library that simplifies HTML document traversing, event handling, animating, and Ajax interactions for rapid web development.
jQuery is designed to change the way that you write JavaScript.
Link : http://jquery.com/
GWT: Google Web Toolkit:
Google Web Toolkit (GWT) is a development toolkit for building and optimizing complex browser-based applications.
GWT is used by many products at Google, including Google AdWords and Orkut. It's open source, completely free, and used by thousands of developers around the world.
Link : https://developers.google.com/web-toolkit/
Prototype:
Prototype takes the complexity out of client-side web programming.
Built to solve real-world problems, it adds useful extensions to the browser scripting environment and provides elegant APIs around the clumsy interfaces of Ajax and the Document Object Model.
Link : http://prototypejs.org/
Dojo:
Dojo saves you time and scales with your development process, using web standards as its platform.
It’s the toolkit experienced developers turn to for building high quality desktop and mobile web applications.
From simple websites to large packaged enterprise applications whether desktop or mobile, Dojo will meet your needs.
Link : http://dojotoolkit.org/
MooTools:
MooTools is a compact, modular, Object-Oriented JavaScript framework designed for the intermediate to advanced JavaScript developer.
It allows you to write powerful, flexible, and cross-browser code with its elegant, well documented, and coherent API.
Link : http://mootools.net/