In those days there was a bit more optimism about such things but it was sort of like "why not just use Linux"? I think, iirc from reading tech news back then, there were also complaints about the quality and quantity of what Apple was releasing in source form.
It was a massive chore to get Darwin 0.1 to build for x86 but it’s possible. And there is 2 things only available as a binary blob, the intel PCMCIA code was never released nor the EISA/PCI adaption layer.
I have some qemu images here:
I guess I care less about a microkernel's advantages for kernel development, than it having non-broken IPC :P
XNU has two sets of syscalls – Mach syscalls (negative syscall numbers) and BSD syscalls (positive syscall numbers). The Mach ones expose the classic Mach "microkernely" API, and the BSD ones provide the traditional POSIX API
The term "syscall" is a bit ambiguous – sometimes it is said that the BSD side has syscalls but the Mach side has traps, other times it is said that BSD syscalls and Mach traps are the two different types of XNU syscalls.
Definitely the BSD syscalls include a bunch invented by Apple themselves (not inherited from *BSD), and I think the same is the case for the Mach traps as well