It's finally out! Yes, Microsoft has again launched it's XML Notepad 2006.
It's not only one of the best XML editing tool but also it's fully written in C# and hey they are also supplying code and design.
XML Notepad 2006 User Interface
XML Notepad Interface Design
So when you download this cool app you will get XML Notepad 2006, it's design document, source code with unit tests!
I'm not going to copy past the features as you can easily get it from links section.
Links:
Microsoft XML home
XML Notepad 2006 Design
Microsoft XML Team's WebLog
It's a great tool to work on, and best of all it's free!
Happy Coding :)