[anexprogrammer]

The Amiga kernel and Intuition (the GUI).

Partly because it was just so damn clean and intuitive. Equivalent Windows apps were an order of magnitude larger, but seemed to offer less.

Partly because each was almost entirely the work of one - RJ Mical for Intuition, and Carl Sassenrath, who would later create Rebol mentioned below, for the kernel.

Lastly the whole was greater than the sum of very excellent parts.

Xwindows and Windows etc were an endless series of disappointments after cutting my teeth on Intuition. I often used to wonder what might have been had it continued to be developed... Or succeeded as it deserved.