Mac OS nanokernel
The Mac OS nanokernel is an operating system kernel that serves as the basis of most PowerPC based system software versions 7 through 9 of the classic Mac OS, predating Mac OS X. The initial revision of this software is a single tasking system which delegates most tasks to an emulator running the Motorola 68000 series (68k) version of the operating system. The second major revision supports multitasking, multiprocessing, and message passing, and would be more properly called a microkernel.