'Jupiter' is the new application model for Windows 8, an XAML (or UI) layer that will overlay programming to help improve graphics, text, and inputs. According to Mary Jo Foley, 'Jupiter' will provide a much smoother animation, typography and bring new media capabilities to Windows 8. 'Jupiter' for Windows 8 will be taking a lesson from the Windows Phone / Zune HD book to improve the user interface, providing a fresh experience to the end user.
After recent announcements from Microsoft about putting Windows 8 on an ARM chip, it appears that Microsoft is bringing the full desktop experience to the tablet, and bringing the tablet experience to the desktop. With ARM chips exploding around the world, Windows 8 could be the first universal OS between a tablet and a PC.