Funnily enough QNX crossed my mind last night for no good reason. The QNX demo floppy is still one of the most impressive demos I've ever seen. On one single 1.44MB floppy they squeezed an OS, a web server, a browser, a text editor, and some other widgets. And the graphical demos would continue to run glitch-free whatever else you did:
This was really quite impressive in '99.