I remember working with QnX back in the mid-90s and found it quite fun (compared to Unix at the time). A friend of mine worked at a company that made commercial X servers and that company's fastest X server ran on QnX (yes, even with the overhead of message passing, it was faster than their Unix version on the same hardware).
That vaguely rings a bell but I don't think I've seen it in action. Pity!
Maybe the future will bring us something like that again, I sure wouldn't mind. The nay-sayers argument that 'micro kernels are slow' seems to be mostly limited to those that have never actually used a micro-kernel based OS for anything. What I remember was - for the time especially - nothing short of astounding performance, 30K slices / second on a lousy 486/33 was not exceptional at all. At the time most other OSs were doing 20 or so...
