"Needless to say, this is no small project and will take a long time to complete; right now, I'd call it somewhere between completely useless and intriguingly experimental. (It runs Skype, at least.) I'm also concerned that if they ever do get it anywhere near useful completion, Microsoft will stomp on it hard.
"That's certainly the high road. But how necessary is it to clone the whole damned OS? A Windows app, after all, is just a block of x86 machine code that makes calls into one or more APIs. If you can clone the APIs in an acceptably clean-room manner, you don't need to duplicate the entire architecture, kernel and all.
"And that brings us to one of the oldest and oddest ongoing projects in open-source computing: Wine, which dates back to 1993, and provides a compatibility layer consisting of clean-room DLLs implementing the Win32 APIs, plus whatever magic is necessary to make the deeper host OS machinery look like Windows to the app"
