Slight clarification, Darwin is a mish-mash of CMU's Mach microkernel, some 4.3 BSD, some BSD userland, some GNU userland (although that seems to be going away)

Slight clarification, Darwin is a mish-mash of CMU's Mach microkernel, some 4.3 BSD, some BSD userland, some GNU userland (although that seems to be going away), and then NeXT/Apple stuff on top of that.