Ubuntu 11.04 Natty Narwhal is the most anticipated version as it will replace Gnome Shell with Unity in the desktop environment. The ‘old’ Gnome desktop environment is now called ‘Ubuntu Desktop Classic’. Natty Narwhal will completely replace the Gnome desktop which was the primary interface used by Ubuntu before the release of the Maverick Meerkat.
Ubuntu 11.04 Natty Narwhal is built on 2.6.37-rc3 Linux kernel with all the development being in house. In this, most Gnome apps have been integrated with Global Menu, except for third party apps like Firefox and OpenOffice.
Ubuntu 11.04 Natty Narwhal is only for testing and should not be used on the production server or the primary server.