[seanvk]

BeOS is another one that comes to mind.

[asark]

That BeOS didn't become a serious, long-term contender in the desktop OS market is a sure sign we're not living in the best of all possible worlds.

[coldacid]

That Amiga never achieved any success outside of niche SFX markets is a sure sign we're not living in the best of all possible worlds. (Although that's more 80s than 90s.)

[AnIdiotOnTheNet]

There's a timeline out there where WindowMaker/GNUStep became the dominant desktop for Linux too.

In many ways, I think the state of modern personal computing is evidence we are, in fact, in the darkest possible timeline for it.

[waz0wski]

If you have not seen it, check out the BeOS-inspired Haiku

https://www.haiku-os.org/

[santafe]

https://www.haiku-os.org/files/get-haiku/ported-software.png

[billfruit]

I think the early to mid 2000s Gnome had that same focus on full functionality presented with simplicity, rarely seen in today's interfaces.

[martinflack]

OS/2 for me.