Apple ripping off Xerox is a well-traveled myth. In fact Jobs & team famously negotiated a walkthrough of PARC, with the specific intention of drawing inspiration from the Star's rudimentary GUI, in return for shares of Apple. They then greatly expanded on those ideas to create their own OS. What Gates did with the Mac OS was similar to what M$ did with dozens of other companies, i.e. finding loopholes & barely-legal means to steal their content, one way or another.