UDE, or the “Unix Desktop Environment,” is best described as “hardcore.” It is not based simply on Xlib (not Qt or GTK+, etc.) and, as such, is incredibly easy to port to various systems. You'll notice that there is no default “title bar” on windows, nor are there close or minimize buttons. Instead, UDE implements what they call “The Hex Menu,” which is triggered by clicking on the window borders. UDE also makes heavy usage of the mouse, going so far as to requiring a three-button mouse in order to use properly.