A number of its Ajax web development tools, including the tools used to develop Google Maps system are available for free, thanks to Google.
http://code.google.com/webtoolkit/ :
Google Web Toolkit (GWT) is a 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; you spend 90% of your time working around subtle incompatabilities between web browsers and platforms, and JavaScript’s lack of modularity makes sharing, testing, and reusing AJAX components difficult and fragile.
GWT lets you avoid many of these headaches while offering your users the same dynamic, standards-compliant experience. You write your front end in the Java programming language, and the GWT compiler converts your Java classes to browser-compliant JavaScript and HTML.

Google Web Toolkit Features
* Dynamic, reusable UI components
Create a Widget by compositing other Widgets. Lay out Widgets automatically in Panels. Send your Widget to other developers in a JAR file.
* Really simple RPC
To communicate from your web application to your web server, you just need to define serializable Java classes for your request and response. In production, GWT automatically serializes the request and deserializes the response from the server. GWT’s RPC mechanism can even handle polymorphic class hierarchies, and you can throw exceptions across the wire.
* Browser history management
No, AJAX applications don’t need to break the browser’s back button. GWT lets you make your site more usable by easily adding state to the browser’s back button history.
* Real debugging
In production, your code is compiled to JavaScript, but at development time it runs in the Java virtual machine. That means when your code performs an action like handling a mouse event, you get full-featured Java debugging, with exceptions and the advanced debugging features of IDEs like Eclipse.
* Browser compatible
Your GWT applications automatically support IE, Firefox, Mozilla, Safari, and Opera with no browser detection or special-casing within your code in most cases.
* Interoperability and fine-grained control
If GWT’s class library doesn’t meet your needs, you can mix handwritten JavaScript in your Java source code using our JavaScript Native Interface (JSNI)
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