I've only ever used QNX in the form of Blackberry products (mostly the Playbook), so I am afraid I don't what the advantages of it would be compared to Linux or something.
I know it's a microkernel which is inherently cool to me, but I don't know what else it buys you.
Can anyone here give me a high-level overview of why QNX is cool?
QNX is hard realtime. At one point, its kernel had O(1) guarantees for message passing and process switching. It could have been rewritten without any loops. I'm not sure if that's still true.
It's also really compact. This used to be a great selling point for underpowered car infotainment systems. Some cars had around 1Mb of RAM for their infotainment, yet they were able to run fairly complex media systems.
QNX is also used for non-UI components, just as a good realtime OS.
Hard real time (so latency guarantees), microkernel (and they actually mean it, so your device drivers can't hose your system), standardized networked IPC including network transparency for all services, ISRs at the application level.