I am fairly sure I remember a Linux desktop back in the 1990s with a moderately-complete classic MacOS look and feel. I think it was called "Sparta" or something like that. I can't find a trace with Google. Not just a window manager like MLVWM. Not just a skin or theme for an existing desktop (like Platinum on Xfce). Functionally, more like Ben Szymanski's "Classic Finder" for OS X.