The Lisa had a custom MMU, if I recall. There were other 68000 based systems that were similar.
My key point is around the operating system. They had a system in LisaOS that had multitasking, memory protection, proper dynamic allocation, etc. It was a better OS than what was shipped on the Mac. It was unfortunate they threw it away. Likely due to personal & organizational politics more than technical and cost reasons (Jobs hated the Lisa). A few years later they were running Mac OS on old Lisa hardware.
My key point is around the operating system. They had a system in LisaOS that had multitasking, memory protection, proper dynamic allocation, etc. It was a better OS than what was shipped on the Mac. It was unfortunate they threw it away. Likely due to personal & organizational politics more than technical and cost reasons (Jobs hated the Lisa). A few years later they were running Mac OS on old Lisa hardware.