Apple is not a monopoly. They may have closed systems, but there's nothing illegal about that. Microsoft, on the other hand has often used and been convicted of using illegal methods to force market share. They use their dominant position to try to block competition, which Apple doesn't use. Also, MS's unethical behaviour goes right back to the start, when Bill Gates used Harvard computers to develop a BASIC interpreter for the MITS Altair 8800 computer. The Harvard computers were not supposed to be used for commercial purposes. Bottom line, Microsoft is a convicted monopolist, Apple isn't.
neither is "monopolistic"
Microsoft has been convicted for it. They are a very unethical company that regularly uses illegal or near illegal tactics to force market share. For a recent example, take a look at how they rammed their OOXML through as an ISO standard. Then look at cases like the recent one with i4i, where they deliberately violated patents, after pretending to enter a deal with i4i.
Back in the DOS days, there was also DR-DOS, from Digital Research, which had features that MS-DOS didn't. However, MS leaned on computer suppliers to not install it. They also put a test in Windows to see if it was running on DR-DOS and then threw up a bogus error message if it was. Digital Research also had GEM for a graphical desktop. There were others, but I don't recall them at the moment.