[AlyssaRowan]

That was Digital Research’s GEM, which Atari had licenced for the GUI of TOS (they threw it together quite quickly). There was a whole thing about GEM and inspiration from Xerox PARC and Apple; that’s largely the reason why the Atari version was the only version that really made it to any kind of brief success.

[steve1977]

I vaguely remember seeing GEM even used on DOS PCs back in the early 90s.

[NikkiA]

It was the only way to use a couple of very early DTP packages (Timeworks being the one I remember).

Of course, by then it was after GEM 2 and had been neutered by the lawsuit which forced it to abandon the desktop metaphor for 2 permanently tiled windows