WPF, Silverlight and Xaml
We just published two specifications today, which you can download from here: http://www.microsoft.com/downloads/details.aspx?FamilyId=3356AF19-A36E-4D6D-9D13-C37DB81EE607&displaylang=en
Learn more about Microsoft's Open Specification Promise (OSP) here: http://www.microsoft.com/interop/osp/default.mspx
Very excited to have them out to the world!
[Update 3/26]
I've created 2 easy to remember URLs to get to either of those specs directly in their PDF form.
Rudi and his Attached Property Rudi considered the following options: binding to a collection, Application