They can be paid or free emulators, depending on their features and category. There exist thousands of such advanced windows emulators for Mac app that let window application to run on a Mac OS. For Mac, emulators can be termed as the grey area because they let window application to run on a Mac and vice versa. But nowadays, emulators are not only restricted to run any particular type of software system rather now the advanced emulators let you run a whole different OS while you are running on a different OS.