1. jQuery: The Write Less, Do More, JavaScript Library

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.

jQuery is really a new kind of JavaScript library, you can write less but do more; maybe jQuery is the JavaScript framework that have the biggest collection of plug-ins and add-ons. Some things you should know:

• Current version: 1.4.2
• Size: 24 KB (Minified and Gzipped) and 155 KB (Uncompressed Code)
• Author: John Resig
• Tutorials in 19 languages: 183 (data on 19 October, 2009)
• Sites in use: 1000+
• Plugins: 3.493 (data on 19 October, 2009)
• Easy to learn
• Support designers very well, by using CSS syntax
• A lots of nice and lovely extensions
• Great community, maybe largest
• Used by millions of website and well known companies like Google, DELL, CBS, NBC, DIGG, Bank og America, WordPress, Drupal, Mozilla etc…

2. MooTools – a compact javascript framework

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.

MooTools code respects strict standards and doesn’t throw any warnings. It’s extensively documented and has meaningful variable names: a joy to browse and a snap to understand.

• Current version: 1.2.4
• Uncompressed Size: 65 KB (client) and 23 KB (server)
• Author: Valerio Proietti
• Using: w3c, cnet, bing, …
• Plugins on Official site: 4
• Better OOP structure
• The animations are smoother
• The syntax and the handle of elements are more logical

3. Prototype: Easy Ajax and DOM manipulation for dynamic web applications

• Lastest version: 1.6.1
• Uncompressed Size: 136 KB
• Creator: Sam Stephenson
• Using: NASA, CNN, NBC, …
• Plugins: 150+
• Better for the big web apps, give you many choices to write custom code

4. Dojo Toolkit: great experiences for everyone
Unbeatable JavaScript Tools
Dojo saves you time, delivers powerful performance, and scales with your development process. It’s the toolkit experienced developers turn to for building great web experiences.

• Lastest version: 1.4
  
• Compressed Size: 26 KB (closely 5.000 code lines)
• Foundation: Dojo Foundation
• Dojo Users: AOL, IBM, Sun, …
• Client-side data storage
• Server-side data storage
• Asynchronous communication

5. script.aculo.us: easy-to-use, cross-browser user interface JavaScript libraries

• Lastest version: 1.8.3 (8 October, 2009)
• Size of Compressed package: 197 KB (including Prototype + Test page)
• Creator: Thomas Fuchs
• Users: Gucci, Feedburner, Ruby on Rails, …
• Documentation wiki & Usage
• Extending the Prototype framework by adding visual effects, user interface controls, and utilities

6. ExtJS: Cross-Browser Rich Internet Application Framework

ExtJS is a very cool cross-browser JavaScript framework for helping you build rich web applications, support all modern web browsers. Plus plenty of plugins and extensions, your ExtJS based web applications become more attractive by features such as well designed, documented and extensible Component model, high performance, easy-customizable UI widgets, …

• Lastest version: 3.1.1 (February 8th, 2010)
• Size of Compressed package: 197 KB (including Prototype + Test page)
• Creator: Jack Slocum
• Users: Gucci, Feedburner, Ruby on Rails, …
• Download | Samples & Demos | API Documentation
• Great components and support

7. UIZE: supporting widgets, AJAX, DOM, templates, and more

• UIZE is open source.
• UIZE is free to use (available under MIT License or GNU General Public License).
• UIZE is skinnable with your own CSS.
• UIZE does not extend native objects.
• UIZE is server agnostic – use it with any choice of server language and platform: Java (Apache TomCat), C# (IIS / ASP.NET), Visual Basic (IIS / ASP), C/C++, Perl (Perl / Apache), PHP, Ruby (Ruby on Rails), Python, etc.
• UIZE has lots of built-in widgets: slideshow, calendar, date picker, slider, marquee, dialog, menu, mag view, etc.
• UIZE offers many powerful features: JavaScript Animation, JavaScript Inheritance, JavaScript Events, JavaScript Modules, JavaScript Libraries, JavaScript Templates, JavaScript Widgets, JavaScript Localization, JavaScript Documentation, JavaScript Code Compression, JavaScript Build Scripts.
• UIZE is in active development, by a core team of experienced programmers.

8. YUI Library: is proven, scalable, fast, and robust

UI is one of the biggest JavaScript frameworks in this list. YUI has all things to help you build interactive web applications using techniques such as DOM scripting, DHTML and AJAX by a set of powerful utilities and controls. YUI has countless powerful features, plugins, extensions that take you the very long time to learn.

• Lastest version: 3 (September 2009)
• Size of Full Developer Kit: 5.7 MB (including Source, debug files, examples, and more)
• Creator: Yahoo! Developer Network
• Sites Powered by YUI: LinkedIn, Wikia, NewsVine, …

9. Archetype

• Lastest version: 0.10.0 (September 2009)
• Size of package: 2.14 MB
• Creator: Temsa & Swiip
• In use: GifTeer, Meteo France, …

10. qooxdoo: the new era of web development

What’s qooxdoo? That’s great and powerfull JavaScript framework to create rich internet applications (RIAs) by taking the advantages of object-oriented JavaScript. qooxdoo includes a platform-independent development tool chain, a state-of-the-art GUI toolkit and an advanced client-server communication layer. It is open source under an LGPL/EPL dual license.

• Lastest version: 1.0.1
• Size of package: 24 MB
• Core Developers: 1&1 Internet AG
• Download | Samples & Demos | Documentation
• Fully-featured graphical user interface toolkit
• Drag and drop capabilities among other components