https://nemanjatrifunovic.substack.com/p/history-of-the-gem-...
He missed out on the recent history of the environment, and at the time, I wrote a blog post adding more info on what happened next:
https://liam-on-linux.dreamwidth.org/96552.html
You do mention OpenGEM and FreeGEM, but not what's in them. They re-added all the features DR removed after the Apple lawsuit. They also added the features from GEM/4 and GEM/5 which John Elliot documented:
There were also other branches of GEM. DR did several...
• ViewMax, which was bundled with DR-DOS 5 and 6. This had Windows-style keyboard controls and could operate and manage DR-DOS's built-in multitasker, TaskMax.
• It also was working on GEM/XM which offered multitasking on plain old DOS.
• X/GEM ran on DR's RTOS, FlexOS. This was the realtime offshoot of DR Concurrent CP/M and Concurrent DOS: a family of full, native, protect-mode, multitasking DOS-compatible OSes for the PC, and 286s, and 386s. FlexOS is multitasking and so is X/GEM.
Some of the code from FreeGEM made its way back into ST GEM. There is a complete multitasking FOSS OS for the Atari ST and compatibles, called AFROS. It targets its own emulator, Aranym.
It originally had a minimal stub ROM replacement to boot the emulator: the OS is a native multitasking one so does not need much from Atari's ROM, which is not FOSS anyway. Atari's ROM is not just a BIOS: it contains the whole OS – the BIOS, and GEMDOS on top, and GEM on top of that.
But the community took that stub ROM and upgraded it to a fullly FOSS replacement for Atari TOS. In other words, with a replacement for GEMDOS and a replacement for GEM. That GEM replacement is partly built from FreeGEM code.
It's a lot of life for a long-dead desktop. I think some of this deserved a mention bigger than a single sentence.