Zorin: Ubuntu based O/S for Windows Users Looking For A Gentle Introduction To Linux.
Link: Home - Zorin OS
Zorin OS features the unique Look Changer program which allows users to change the user interface at the touch of a button. Simply click on either the Windows 7, Windows XP or Linux's GNOME interface in Zorin OS Core and Educational and your desktop looks and behaves accordingly. The Premium versions (Zorin OS Gaming, Multimedia and Ultimate) also include the Mac OS X, Windows Vista and Windows 2000 looks.