Early 90's, especially on Amiga -- where a proper windowing desktop env ("workbench") coexisted with the wildest custom UIs. Maybe it was the roots of the machine, heavily used as a games console and a demoscene workhorse? It seems like at that time there was so much creative design effort put into UX -- and it didn't seem to get in the way, maybe because each genre of software was kind of on the cutting edge back then, establishing what would eventually evolve into conventions. Mod trackers, image editing, disk copying, etc. Maybe it's a bit of nostalgia, but it felt really immersive to pull up a piece of software you were familiar with; each UI was so distinct and purpose-built, but it also had.. flourish? style? soul? Not so much now.