[CrimsnBlade]

I wouldn't be too afraid of the Linux GUIs. With the amount of customization that is available for these you can probably make it operate very similar to the way your OS X GUI does. Granted that could take some extra work on your part.

[squeaky-clean]

It would take a ton of polish that I don't believe any non-corporate team could accomplish. There is elementaryOS, which is my favorite Linux distro. It's absolutely beautiful and looks a lot like OSX, but OSX is still much more enjoyable to use, for reasons I can't exactly specify.