XAML stands for Extensible Application Markup Language and is used extensively with Window Presentation Foundation (WPF) and Windows Workflow Foundation (WF).  Lester Lobo has created a great tool for previewing XAML code called XamlPadX.  I have not played with it too much, but what I have seen so far I like.  If you are working with XAML and don’t have the money to spend on Expression Blend, I recommend giving this tool a try.

It is easy to install.  Simply take some XAML code and paste it in the application.  You get immediate feedback.  Very nice.