Just for comparison the Acorn Archimedes launched in 1987 with Arthur OS (later to become Risc OS) with a full windowed desktop with overlapping windows etc. They were able to pull this off because they had designed a new processor that they called the "Acorn RISC Machine"*
Yeah that drag and drop save was funny. It was the era of 'lets do this using drag and drop just because it looks cool and metaphorical - you are literally PUTTING that file IN that folder - geddit?'
I don’t agree that it was eccentric, I used these as my first machine and they felt pretty natural. I would also suggest that these interactions weren’t completely standardised at that point.
- "we have a three button mouse, we're going to make use of all of them" as opposed to Apple
- instead of file pickers, saving was done by drag-and-drop: press save and a window pops up with the file, which you drag to a target folder.
The !Application system, an early bundle mechanism, was a simple and effective form of packaging without having to do anything fancy.