Google Web Toolkit
Google Web Toolkit (GWT) is an open source Java software development framework that makes writing AJAX applications like Google Maps and Gmail easy for developers who don't speak browser quirks as a second language. Writing dynamic web applications today is a tedious and error-prone process.GWT supports a variety of built-in Widgets that are useful for AJAX applications, including hierachical trees, tab bars, menu bars, and modal dialog boxes. GWT also has built-in support for remote procedure calls and other more sophisticated web application features.
They released the GWT 1.2 and now used to develop and debug with GWT on Mac OS X in addition to Linux and Windows.
more can be learned in:http://code.google.com/webtoolkit/