How to open UMLet's "uxf"-files with a double-click in Windows?
Associate the "uxf"-Files with umlet.bat. To assoiciate it, right-click any "uxf"-File, select "Open with" (or if this is not available "Open" and "Select from List"), choose umlet.bat (in the directory com.umlet.plugin) and select "Always open with this program".