QNX is on of those OS's I'd love to need. I first saw it at '89 Comdex (remember when that was cool?) and thought it looked kinda neat. Then I read about their micro-kernel design in the 90's and thought it was really cool. Right around 2000 they had a demo floppy that had the Kernel, IP stack and a GUI brower all in 1.44MB. BTW it was real time mutli-tasking too.
Anyway, I have never had a really good excuse to buy it, but I keep hoping someday I will.