A tool that compiles JavaLanguage to JavaScript, thus supporting static typing and automated optimizations and automatically provides hooks for multi-browser compatibility.  

This is performed for many of Google's AjaxWebApplications.

http://code.google.com/webtoolkit/overview.html

From that page:

	 :	Writing web apps today is a tedious and error-prone process. Developers can spend 90% of their time working around browser quirks. In addition, building, reusing, and maintaining large JavaScript code bases and AJAX components can be difficult and fragile. Google Web Toolkit (GWT) eases this burden by allowing developers to quickly build and maintain complex yet highly performant JavaScript front-end applications in the Java programming language.

Features: very extensive - including such goodies as integrated library support for internationalization, easy RPC, suggestion boxes, and effective use of the 'Back' button and bookmarking/history even with the surrounding AJAX difficulties.

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See: http://code.google.com/webtoolkit/doc/1.6/RefWidgetGallery.html - Widget Gallery (version 1.6)

[EditHint: Merge with GoogleWebToolkit]

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See also: BrowserAsGuiAssembler