Stefan,
Thanks for the reply. I completely understand the instructions. However...
When downloading is in progress, it shows as a .zip extension. Upon completion, it simply reads Fret_Board_Maker - no shown extension when opened in Downloads folder. So, I add ".vgadget" extension and try anyway. Open Aspire, select "Install New Gadget" and click to open from downloads folder. Double click the renamed folder Fret_Board_Maker.vgadget to open, and it simply opens that folder (rather than loading), showing no contents (Aspire does not see any contents, as it's looking for Vectric Gadget Package Files, which the folder does not contain). Don't know why it disregards the renamed file, only opens it.
Okay, let's take a closer look.
When opened outside of Aspire, folder contains: another folder labeled Fret_Board_Maker (no extension, right click, no option to rename), LUA file, License, and sample JPG.
Upon opening that folder (Fret_Board_Maker again, no .zip extension and no ability to rename) I find Fretboard_Parameters3D, a Chrome HTML document which I can open outside of Aspire and the calculator appears, and is functional. Is it the Chrome HTML document that needs to be renamed, since it does not work on the zip file it is contained in? (doubt it, but I'm flailing at this point).
Sorry to be a pain - this just is not making any sense at all, since there is no ".zip" extension once the folder is sitting in the Downloads folder. Only indication of it being a zip file is the zipper on the folder's icon. I've downloaded numerous times in case of corruption during downloading.
Any other suggestions?
(other than give it up, I'm beyond help...

,)
FWIW, Windows 10
jeff