ZK is an open-source Ajax Web framework that enables rich user interface for Web applications with no JavaScript and little programming.

script.aculo.us provides you with easy-to-use, cross-browser user interface JavaScript libraries to make your web sites and web applications fly.

The Solvent is a cross-browser AJAX application toolkit written in JavaScript. The Solvent is provided as modules or as an entire toolkit. The projects focus is to promote robust web applications and enable rapid web development.

Sajax is an open source tool to make programming websites using the Ajax framework — also known as XMLHTTPRequest or remote scripting — as easy as possible. Sajax makes it easy to call PHP, Perl or Python functions from your webpages via JavaScript without performing a browser refresh. The toolkit does 99% of the work for you.

Zapatec AJAX Suite includes mature, feature-rich widgets to cover all your development needs. Modular architecture gives you the flexibility to use a few widgets today and migrate to using the full suite on an as-needed basis. No need to learn a proprietary XML dialect or a complicated new platform — use the same tools you currently do, like HTML, CSS, JSON and more.

PlotKit - Javascript Chart Plotting is a Chart and Graph Plotting Library for Javascript. It has support for HTML Canvas and also SVG via Adobe SVG Viewer and native browser support. PlotKit is fully documented and there is a quick tutorial to get you started. PlotKit is a complete rewrite of CanvasGraph. It is better structured and supported.

TurboWidgets are JavaScript client-side controls that provide a rich user-interface experience for AJAX-style web applications. Built on top of the popular Dojo Toolkit, TurboWidgets are designed for ease-of-use and flexibility.

moo.fx is a superlightweight, ultratiny, megasmall javascript effects library, to be used with prototype.js or the mootools framework. It’s very easy to use, cross-browser, standards compliant, provides controls to modify any CSS property of any HTML element, including colors, with builtin checks that won’t let a user break the effect with multiple, crazy clicks. Optimized to make you write the lesser code possible, the new moo.fx is so modular you can create any kind of effect with it.

Kabuki (a.k.a Zimbra) AJAX Toolkit is a client developer library, similar in style to traditional object-oriented widget libraries like Eclipse’s SWT, albeit for JavaScript.

jQuery - New Wave Javascript is a fast, concise, JavaScript Library that simplifies how you traverse HTML documents, handle events, perform animations, and add Ajax interactions to your web pages.