There is only one file type that uses the .XNT extension:
QuarkXPress Extension File
Application extension used by QuarkXPress, a program used for professional publishing; extends the functionality of the default QuarkXPress application; used for adding new components to the user interface, importing and exporting new file types, enhancing application workflows, or adding other functions.
Several XNT files are included with the QuarkXPress installation. They are located in the /XTensions/ directory. To disable an extension, place it in the XTensions Disabled directory.
Updated: September 7, 2010