Wikipedia
MacMach
MacMach is a computer operating system from the early 1990s, developed by Carnegie Mellon University. Architecturally, it consists of 4.3BSD code running on the Mach microkernel, with the Macintosh System 7 running experimentally as a Mach task. The entire system runs on Macintoshes based on the Motorola 68k family of microprocessors. Its license requires the user to have an AT&T UNIX license, in addition to Apple, Inc.'s restriction against further redistribution.