Interix/SFU/SUA/whatever - I tried, REALLY TRIED, to make it work so I could build things with it. But X11R5 was just TOO out of date, and autotools didn't have the capability of handling the lack of compatibility. And writing those changes myself proved to be a frustrating (if not impossible) task.
Didn't even have 'tar' - only 'pax', and pathetically didn't support a lot of things (like compression).
I gave up on it. Cygwin just works better.
As for Windows NT needing 16Mb of RAM: compare that to Win-10-nic, which seems to run poorly with 100 times as much RAM... especially 'the Metro' / UWP garbage.
I had the unfortunate experience of having to create a virtualbox VM running Win-10-nic to test an application on. I had an easier time installing the latest ReactOS (multiple crashes, and looping in the 'OOBE WELCOME' menu thing. After (effectively) disabling audio (switched to the AC'97 driver, which apparently isn't supported at ALL), I was actually able to install it. Then I went to give MS feedback on how pathetic something worked, and the performance of the UWP text box was SO bad, I coudl type LITERALLY! TWICE! AS! FAST! as the text rendering of what I'd typed. Meanwhile, CPU on _TWO_ _CORES_ was being _MAXED_ _OUT_ the _ENTIRE_ _FREAKING_ _TIME_!!!
I'd take that old clunky NT 3.1 *ANY* day over CRAP-WARE like Win-10-nic.
Oh, and my windows application ran JUST FINE (even though I had to test it to make sure). I'll need to fire that thing up ocasionally to test it out AGAIN and AGAIN, of course. But I think I'll "unplug" the virtual network drivers when I do it, so that it doesn't spend unnecessary time and bandwidth UPDATING itself whenever I do it... and use a diskette or CD image to transfer the application EXE file whenever I test it. Heh.