Back in the 2000s MS agreed to port Office and Internet Explorer to the Mac. This was a good move for both companies. Bill Gates appeared on screen during an Apple Conference to talk with Steve. Huge boos. Steve had to work the crowd back from the ledge.
Then Office and IE were ported. It was so weird running Word on a Mac. It was a good port too. They did a good job of embracing Mac UI ideas. I found the Mac Word better than Win Word.
I was kind of new to the Mac back then.
I imagine Apple donated a bunch of early OS 10 machines to MS for development. I wonder if the MS Mac Dev team was a pariah at MS.