I remember the QNX Demo on a 1.44 MB floppy disk. It booted straight into a full blown window manager and had a basic web browser. That was 1999 and I never saw anything like that afterwards.
The first time I booted menuet OS (2005? high school?) I was absolutely floored at how capable (and decent looking) an OS that lives entirely on a 1.44mb floppy could be.
https://news.ycombinator.com/item?id=38059961
https://news.ycombinator.com/item?id=27249075
That was 1999 and I never saw anything like that afterwards.
Now you have ;-)