Free AJAX Toolkits, Frameworks, Libraries and Source Code

Google Web Toolkit - Build AJAX applications in the Java language

Google Web Toolkit helps you in developing AJAX web applications like Google Maps and Gmail by taking care of many of the browser dependencies under the hood. Your applications are built using Java, and the toolkit translates it into JavaScript and HTML that works across a number of browsers, including IE, Firefox, Opera, Mozilla and Safari. You can also intermix JavaScript into your code. Other features include the ability to create widgets and lay out widgets, debug your applications using advanced Java debugging facilities, simple remote procedure calls (RPCs), automatic management of the browser's back button, etc.

Yahoo! User Interface Library

Yahoo! supplies a number of utilities and controls for use in your AJAX and DHTML web applications. They are released under a BSD licence. The library is written in JavaScript. The library features a calendar, containers (which includes tooltips, dialogs, etc), menus, sliders, treeviews, autocomplete, a drag and drop utility, an animation utility, CSS fonts, CSS page grids, and so on.

Yahoo! Design Pattern Library

The Yahoo! Design Pattern Library features a variety of patterns, which are defined by them as optimal solutions to common problems. Each problem comes with text describing the solution. Among the many patterns described are animation transitions, collapse transitions (such as when you want to collapse an item on a page), dim transitions, expand transitions, fade-in transitions, self-healing transitions, slide transitions, spotlight transitions, page grids, tool tips, hover, etc.