Some people may gripe about QNX being inflexible and difficult to use. However, there is one reason QNX is a kickass operating system (besides being super fast and super compact). It's stable. Very stable. Like so stable it is fault tolerant and suitable for situations where failure of the OS could result in death or injury. Check our this excerpt from their developer EULA:
Unless QSSL has provided you with express written consent, the Product may not be used in any application in which the failure of the Product could lead directly to death, personal injury, or severe physical or property damage (collectively, "High-Risk Activities"), including but not limited to the operation of nuclear facilities, aircraft navigation or communication systems, air traffic control, weapon systems and direct life support machines. QSSL EXPRESSLY DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY OR CONDITION OF FITNESS FOR HIGH-RISK ACTIVITIES. (emphasis added)
Microsoft, Apple and Linus Torvalds won't ever say you can get written consent to get around this disclaimer. In fact, they'll expressly deny that they can do this or make that kind of offer (read the EULA's). However, pay for the proper license and the right product, and QNX can promise this kind of stability. That's one reason it's so expensive.

At least, that's what I was told.