You've heard the Ivory soap slogan, "99 44/100 percent pure". Until today you could say much the same about the Google Web Toolkit (GWT). While most of GWT was open source, a few important pieces were binary-only. Today that all changed as Google made the entire GWT 1.3 Release Candidate available, with source, under the Apache 2.0 license.
GWT was introduced 7 months ago as a radical new way to develop Ajax applications using an old familiar language - Java. It enables developers to use all their great Java tools and expertise to create "no-compromise" web applications. According to Google's Making GWT Better page,
One reason Google created GWT was so they could use it for their own applications. Programs like GMail are incredibly hard to write because of subtle (and not-so-subtle) differences between browsers. While they're not intending to rewrite GMail any time soon, GWT developers have been dropping hints about new public-facing Google applications in the works now that will be leveraging the toolkit. With GWT itself being open source, those applications can benefit from the resources of an entire community, and the community can benefit from the resources of Google.
So why wasn't GWT completely open source to begin with? According to Google,
We weren't quite ready to open source the whole thing immediately because we knew we had plans for major infrastructure work (like Mac OS X hosted mode), and we really wanted to encourage everyone to focus on the idea of the product itself and how to write apps instead of creating distractions having to do with GWT's open sourceness. GWT took off much faster than we expected, and it quickly became clear that the most sensible way to advance GWT quickly would be to open it sooner rather than later.
Bruce Johnson, GWT tech lead, says that Google is committed to "doing this the Right Way". From now on, he says, all GWT development will be done in the open, directly from the GWT project on Google Code. From the web site: