This tool allows for comparison of different XAML dialects and utilized framework namespaces. Want to know if your Silverlight project will translate well to Windows 8 Metro? And whether your Metro assets can be reused in your Windows Phone app? And how about that WPF app?
This helpful tool provides some interesting metrics. Note that it only compares types/classes and all their members. It makes no comparison of behavior differences between classes and members of identical names.