The origin story of the GEM stuff is quite interesting. Lee Lorenzen was an employee at Xerox in Texas, and wanted to get some of the ideas from the Star onto commodity 8080/8086 hardware (just prior to IBM PC, still in latter stages of the CP/M era). He made a prototype, presented it, and it went nowhere. Gary Kildall (DR) then recruited him to come work for them doing basically that. He (Lorenzen) later went off to spin up his own company -- which created Ventura Publisher, which was built on a fork of GEM.

You can see Lorenzen's original pitch to Xerox of his "LoneStar" prototype here: https://www.youtube.com/watch?v=EMBGRZftS30

I believe he has gone on since to be involved in venture investment.

GEM maybe has a bad reputation as a bit of a Mac UI knockoff, but the history is actually deeper than that. Like a lot of things DR did, it got a bit neglected on the market.

Atari Corp also did a bad job of ongoing maintenance of this stuff. At least not until the latest-80s/early 90s when they suddenly started to iterate on it, hired Eric Smith (author of "MiNT" a unixy multitasking kernel that built overtop GEMDOS) to work on the OS, and pushed out proper multitasking versions... for their 68020/030 machines ... but too late.

It'd be cool if Landon Dyer (who is a user here) were to comment on this, as he was on the team that ported all this stuff from x86 to 68k. Unfortunately it looks like his blog where he wrote this up (dadhacker.com) seems to be gone (!?), it was great writing.

I also believe some of the sources from GEMDOS were used as part of the DR-DOS source tree later. All of this is GPL now.

The ability to fairly easily port MS/PC-DOS software to the Atari ST could have been a "secret power" for the ST, but didn't really pan out. The ST did have the ability to work with PC floppies and filesystems, and that was super useful. I recall we were promised ports of e.g. Lotus 123, and MS Word, and neither became a thing. Well, Word did (MS Write) but it was a hot mess (https://www.atarimagazines.com/startv3n1/microsoftwrite.html), and there were better indigenous word processors already.

Also interesting, before the ST was ready, the 68k port of GEM & GEMDOS was run on Motorola VME 68k machines, but also on the Apple Lisa. The article touches on this, but seems to think the Lisa port was not completed, but it actually was, and the has since been resurrected, and boots:

https://github.com/cheesestraws/lisa-gemdos

https://stardot.org.uk/forums/viewtopic.php?t=20964

https://68kmla.org/bb/index.php?threads/gemdos-on-the-lisa-c...

Finally, the (GPL'd) EmuTOS team has basically done all of the heroic work of porting the original DR sources to the Atari ST again, based on the original DR sources. And they have done an amazing job of reproducing Atari/DR's work faithfully.

https://emutos.sourceforge.io/

So the Atari ST now has a fully open source GPL'd operating system stack.

That, and EmuTOS runs lovely on other 68k machines (Amiga, Mac, and Lisa for example) as well as ColdFire machines (the "FireBee" Atari-ish computer, and dev boards). It's a great little 68k/ColdFire operating system that is quite portable and well supported. If you build out a 68k or ColdFire based board it is a good choice as an OS.

EmuTOS running on Amiga: https://www.youtube.com/watch?v=uxIytWnqQnU