Shadows
in its basic level is free.
It comes with a powerful set of functions and a full documentation. If you want to discover further functions, you can acquire a license of Shadows Expert or Shadows Pro.
Shadows Expert
is a level dedicated to people who want to access to more advanced functions in the program. Shadows Expert adds to the basic version the analemmatic and cylindrical sundials, the ephemeris tables, a several new drawing options on sundials, such as Italic and Babylonic hours, the ability to insert images on the sundials, some export functions, and others.
Shadows Pro
is the most advanced level and is made for professional sundial makers and power users. Shadows Pro adds on to of Shadows Expert the planispheric astrolabe, the vertical declining analemmatic sundial, the bifilar sundials, the drawing of azimuth-altitude lines on the sundial and in a separate graph, the export of the drwaing in WMF and DXF (AutoCAD)...