Least PC-Compatible MS-DOS machines?

Got my GRiD Compass 1101 working this week (got distracted from my ASR-33 repair, what can I say, I'm easily distracted) -- replaced a couple of bad RAM chips and it's up and running again. It boots to the GRiD version of MS-DOS 2.00 from the internal bubble memory, so I've been playing around with that a bit, digging through my old DOS archives looking for stuff to run on it. I can't find a single non-trivial DOS program that runs successfully on it. This isn't altogether surprising as the Compass was never intended to be a PC compatible machine, the MS-DOS port was an afterthought. Still, it seems considerably less than useful. Which leads me to the question -- what was the least PC-Compatible "MS-DOS" machine out there back before "100% PC Compatible" was a thing? The Compass has a lot going against it, as the only thing making it close to PC compatible is the 8086 CPU -- everything else is completely different (bitmapped display with no character modes, bubble memory for internal storage, GPIB disk interface, a 70-something key keyboard missing a lot of PC standard keys... I'm not sure about more esoteric things like interrupt controllers, etc.) At least the disk controller uses a standard 360K format compatible with the PC, so data interchange was fairly straightforward... What say you? - Josh