I went to a computer show in Toronto around the early 1990's where QNX had a large booth. They emphasized the stability of the system. It was being used in nuclear reactors, military ships, ATM machines, traffic light systems, etc... Areas where stability over long periods of time where extremely important. Imagine trying to control a nuclear reactor with windows constantly freezing up and crashing on you.
Most impressive was a demonstration of upgrading the QNX OS while apps were running without needing to close the apps or shut down. You could see the appearance of each apps interface change as it moved the apps to the updated OS. All the running apps had to be written in a manner compliant with this feature, but it was still very impressive.
