Enlightenment is a window manager for X. It´s design goal is to be as configurable as possible - in look AND in feel. Currently in the look department it pretty much has that done. you can design your own window borders, menus, and other elements of your screen to look any way you like. You don´t have to touch one line of code and you don´t have to recompile anything. It merely involves being able to use an image drawing program like GIMP and edit some configuration files