Silverlight 2 released a few weeks ago. There were a few controls that were missing from the release however. Microsoft didn’t forget about these controls, instead they worked on them out of band and released them as a CodePlex project. This is becoming a common pattern in the development of frameworks at Microsoft. The CodePlex projects eventually get merged into a future release. Here is what Microsoft has to say about this pattern.
We use an iterative, evolutionary development model to release new controls and updates often and get feedback from the community to our development team quickly. With access to source code, unit tests and the infrastructure magic we use internally, the community can let us know what it likes and what it wants to change. Anyone can download the source code and start exploring. This transparency will allow the community to help us prioritize features based on real-world usage and actual customer scenarios. We also want to make it easy to reuse skills and source code which is why all our components are designed with Windows Presentation Foundation in mind and the Silverlight Toolkit is released under the Microsoft Public License.
Learn more http://www.codeplex.com/Silverlight
The Silverlight Toolkit is a collection of Silverlight controls, components and utilities made available outside the normal Silverlight release cycle. It adds new functionality quickly for designers and developers, and provides the community an efficient way to help shape product development by contributing ideas and bug reports. This first release includes full source code, unit tests, samples and documentation for 12 new controls covering charting, styling, layout, and user input.
All Source code is available. You are granted a license to use the controls, edit and extend the source code.