The Ubuntu default desktop uses the Gnome window manager, but there are a number of different window managers that can be installed, including KDE, Xfce, Blackbox and Fluxbox.

Installing Enlightenment is a simple process. You will want to make sure that you have selected the alternate install repositories.

Open a terminal window and use the following command:

sudo apt-get install enlightenment

Once the install is complete, log out and click on the Options button in the lower left hand corner:

You will see a menu listing all of the window managers installed on your system. Select Enlightenment from the menu, and continue to log in.

Hitting the Win+Alt key combination should bring up this menu(at least it did for me), which will show you how to interact with the desktop:

For instance, clicking the middle mouse button will bring up this menu, used to launch apps, etc.

Right clicking the desktop will show you the settings menu, with quick access to various desktop settings:

Here's a full screenshot of the default desktop:

For more information, check out the Enlightenment homepage.