The Yellow Box lives on in a way; Safari for Windows is very much based on a Cocoa runtime for Win32.<p>Safari even ships with some obviously named DLLs which can be used to link basic (non-UI, mostly) demo CoreFoundation-based apps out-of-the-box with the headers from OSX dropped into mingw.<p>I was trying to reverse-engineer the Safari DLLs enough to make GUI apps work a few years ago, but a combination of shifting priorities and a cease-and-desist letter from Apple led me to pursue other things instead.
I still have WebObjects 4.5.3 on my home machine installed (Windows XP). It's basically OpenStep for NT (YellowBox?) - it kind of works, but I haven't done much in it.<p>WebObjects 5 moved fully to Java.
If I knew what I know today about Objective-C and OpenStep back when I was fighting with COM and Win32 in the 90s, I would have been a very enthusiastic Yellow Box/WinNT supporter.