One of the surprise hits of my collection of ebooks is "Inside Generic CADD 6." This is a book I wrote for WordWare Press back in 1993 under the title of "Learn Generic CADD 6.0 in a Day." The publisher had an entire series of "Learn in a Day" books, and I wrote for them about AutoCAD, AutoCAD LT, Visio, and Generic CADD.
(Recall that Autodesk bought Generic CADD, turned it into Autodesk Retail Products, and then under Carol Batz shut down the division. AutoCAD LT became the intended replacement for Generic CADD users, who may well want to use the General CADD Pro workalike instead.)
Once the Generic CADD book stopped selling, I obtained from WordWare the copyright for it (along with the copyrights for all the other books I wrote for them), and then in 2002 turned it into an ebook. Every few months, I am again pleasantly surprised when someone buys a copy (from here). I suspect it is mostly for nostalgic reasons. After all, this is what the UI looks like:
I have been using Gcadd6 since it came out, now running it on DosEmu on a 32-bit virtual
machine under 64-bit Linux. (It won't run under DosEmu 64-bit.) I have LONG since lost the book and there is still something occasionally I have forgotten or never used.
I switched to Linux before XP came out, but also tried Generic CADD under XP without success. But it works really well under Linux/Dosemu (32 bit). I think probably the authors of Gcadd took some liberties with the video calls, which the emulator for real-mode code under 64-bit Linux does not support -- no emulator is necessary for 32-bit; there is hardware support through the virtual-86 mode, which is not available when running 64-bit.