Pear OS is an Ubuntu 12.10 based Linux distro with a Mac-like skin.
They just released version 7 and I took it for a spin. It definitely apes a lot from Cupertino.
From start up, login, launcher, Finder, to even Mission control, this distro is a definitely Apple-inspired. It even has a time machine app called "Back in Time."
Overall, it doesn't work quite like OSX. It is still using GNOME 3 with a skin.
Still, it is an interesting release.
Screen shots for your perusal:
On a 2560x1440 display.
Time Machine backup.
And here is how it looks on a 27" iMac.