I think "OroboroSX", or some such name, is an X window manager for OSX that makes X apps fit in with Mac apps so it's not obvious which style is running. Gtk and Motif have been ported, so the GUI is not a big issue. The audio side is still primitive, but easy to use. Porting Snd took a few days, mostly spent chasing down dumb things like the -framework loader switch. I'd say it took about the same effort overall as porting to the Sun.