Nothing's stopping you from making classic MacOS that OS – infinitemac.org is a tremendous website full of emulators with a large software collection and drag and drop file transfer! It has very good ergonomics if you just want to play around with it, throw some software you downloaded on to it, etc. When coding for the very early Mac, you just targeted a B&W 512x384 display.

The Macintosh Toolbox is a bit verbose, though.