A few months after the release of Silverlight 3, Scott Guthrie announced the availability of Silverlight 4 Beta at the PDC. And what we can say, it’s that this version is full of features that the community has been asking for:
For more information on these functionalities, you can read the Tim Heuer post about that: http://timheuer.com/blog/archive/2009/11/18/whats-new-in-silverlight-4-complete-guide-new-features.aspx
To download the runtime: Windows or Mac.
The official web site: http://silverlight.net