If Microsoft hadn't been around Apple would have probably defined the early PC era. The Apple II was released in 1977, 4 years before IBM decided to enter the home market with the PC.

Or Commodore might have been the one to dominate. They sold about 5 million Amigas.

Or it could have been NeXT after Jobs was forced out of Apple and started a new computer business.

The winner turned out to be Microsoft, but desktop computers were well on their way to being a standard thing long before Microsoft / IBM got into the market.