@thomasfuchs I don't _think_ that was it. I have this distinct memory of wiggly (sine-wave like) colorful window borders that looked like tubes as one of the demo screenshots. Not suggesting that that is what the OS would look like but that you could _make_ the OS look like that.
Digging a little more, i think this was _just_ before rhapsody. It's what they were working on when they were still debating if they should buy BeOS or NeXT.