I feel I was lucky because I learned computing on a QNX system in High School. The people a year younger than myself ended up learning Turing on early Windows systems. I couldn't understand why Windows on a more powerful machine was so featureless and had lousy graphics in comparison to the "lesser" QNX terminals I learned on.

Also, it seemed unreasonable that QNX could be contained on a single floppy diskette, but you couldn't come close to running a single floppy Windows instance, and DOS was totally braindead in comparison to QNX's command line.

Needless to say when Minix and then Linux came around, I was fully on board.

Can someone please explain to me what is so powerful about QNX ? I keep hearing about how great it is, but haven't really seen concrete proof.

I'm not sure claims that it's "great" are that common, but it's interesting because it's a quite pure microkernel OS, can be extremely light and is commonly used in real-time and safety-critical environments. Personally, having used it a few times, it has some quite nice parts, but its development and support aren't keeping up sadly.

Mostly because it is small, posix compatible and realtime.