Odd it doesn't do much on the Atari ST lineage really apart from mentioning it. Lots of articles seem to have this problem.

There was a lot more going on in the 68k / Atari ST line than on PC, in the end.

In the 90s most of that was in Germany though. Read up on "Magic" OS sometime.

And these days, the modern variant of GEM is really EmuTOS and also Xaaes on the ST line.