The Google Web Toolkit has been open-sourced. The toolkit was developed internally and can be used to create products like GMail and Google Maps. It allows you to program in Java and let the GWT compiler convert your code to browser-compliant AJAX and HTML (see this page for more information).
This is a smart move by Google and is further show of their efforts to woo developers. It follows their release of a project hosting site on Google Code this summer and their many APIs (the latest of which was for Google Spreadsheets). It’s smart for several reasons. First, Google is well-known for being a huge consumer of OS software and have been criticized in the past for not contributing back — I don’t think anyone could say that now. Second, Google gains from developers using their APIs and building mashups. Tools like GWT and Code assist developers in their efforts. Third, what better way to be able to hire developers that can hit the ground running than by letting them teach your internal tools on their own time?
Update: I originally stated that GWT was used to create Gmail and Google Maps. That was incorrect and I have corrected the copy above.