Apple is releasing their Local Integrated System Architecture (LISA) OS as open-source next year. If you recall, the Apple Lisa didn’t sell well at all, as a matter of fact it only sold ~10K units. However, it was the first PC to have a GUI and use a mouse.
Just think if Apple didn’t sell the thing for many times that of an IBM PC and we might have the Apple OS as the defacto standard now. You can check out the announcement here. If you really want to go down memory lane you can check out this old Apple Lisa commercial below.