As I understand it, it's supposed to be a from-the-ground-up reimplementation of NT5 / Windows 2000 with maybe a handful of later tech squeezed in. Historically, it has borrowed heavily from the WINE project, though I'm not sure of the current state of play. It would certainly make sense to have continued to do so.

It's intended to be compatible with any and all Windows software, but the goalposts keep moving and the number of steps they are behind increases faster still. At this point it's barely more than a passion project for the devs, though many of us really want them to succeed.

(See also Haiku, which is a reimplementation and advancement of the contemporaneous BeOS.)

I've occasionally tried to get ReactOS to run in a VM for the nostalgia and to see something like the screenshots, but it never seems to work for me, not that I've tried this new version yet.

ReactOS is still in very early alpha and can not be comfortably run on bare metal systems except for some from the late 90's or early 00's.