XAML Cruncher is an interactive XAML experimentation tool. Type in the XAML and see the object. The program was obviously inspired by Chris Anderson's XamlPad (included with the SDK) but XAML Cruncher has all the "features" of Windows Notepad, including File Open and Save dialogs, a font dialog, XAML source printing, and customization of layout and startup document.
XAML Cruncher is installable through the .NET ClickOnce facility from the Applications = Code + Markup page of my web site.
All source code for XAML Cruncher will be included with the book. (Actually, you'll probably be able to download the source code from the Microsoft Press web site without buying the book, but you'll have to live with the guilt.)
Any bugs or feature requests, let me know at firstname.lastname@example.org.