Ask HN: What operating systems, apps, etc. had your favorite UI designs?

I enjoy looking at the UIs of older platforms or software. Something about that pixel-ish look appeals to me more than the modern look of UI.

For me, one of my favorites was the look of some of the later PalmPilot UIs. They were surprisingly good for a display of only 160×160 pixels. They may not look the best today, but they were very functional. In some ways, I actually prefer older UI designs. Modern UI components feel more complex and, in my opinion, lead to a greater number of bugs.

What are everyone’s favorite UIs, old or modern?