So OpenStep for Windows NT ran under windows NT and it looked like Win32 GDI but it wasn't Win32 GDI. It was still display postscript but the GUI elements (NSButtons, etc) were themed to look like Windows NT instead of NextStep. For whatever reason they were included in Mac OS AppKit as well.
I never knew about this and was a NEXTSTEP/OpenStep/Rhapsody/OS X user and spelunker. Tell me more!