It&#x27;s called Darwin: Mach + kernel-mode components for things like graphics and networking + some modifications. Mach used straight-up as a microkernel wouldn&#x27;t have been fast enough. I&#x27;ve heard people on their developer side admit Mach was a mistake and want to ditch it. Just would be hard at this point.<p>Animats and I both thing QNX was the best microkernel of the period, used successfully from embedded to [briefly] desktop prototypes. Managed to get microkernel advantages while being <i>fast</i> and deterministic. People working on new one&#x27;s should take lessons from them. INTEGRITY RTOS&#x27;s have some nice design choices, too, like making apps donate their own resources to kernel functions they call and using only predictable instructions in critical paths.<p>Mach is crap compared to the competition. Despite all the attempts to make it not so.