OS/2 (ok, technically it does kinda-sorta still exist, but for all practical purposes it's dead)
No 'tisn't - https://www.arcanoae.com/ At the very worst they already have a bunch of drivers for relatively-modern hardware: https://www.arcanoae.com/shop/os2-ecs-drivers-software-packa... However, if their promises to release a semi-modernized OS/2 actually come to fruition I'll be really happy. :D
At this point, I'd settle for a really good implementation of the WPS on Linux. I don't care that much about the OS/2 API or SOM or any of that stuff. But the UI experience hit a sweet spot for me.