Of all time? Amiga Workbench 2.1. Loved it! So ahead of its time. *drops mic and walks off stage*

DEC VAX VMS

Amiga Workbench 2

AmigaOS ruled the world for a time... And then FreeBSD

And we have a winner - Amiga was so far ahead of its time that OSs are still catching up with some of its concepts and feature set.

I loved Workbench 1.3...

Hey you got it on the picture right there!

My father-in-law has a similar phrase. If he doesn't know, his response is usually, "Let's find out!" At which point, his wife typically cringes and the "kids" whoop and head out to his shop.