http://www.dcs.warwick.ac.uk/~john/sw/sawmill   

 Sawmill is an extensible window manager using an Emacs Lisp-like
 scripting language--all window decorations are configurable and all
 user-interface policy is controlled through the Lisp language. This
 is no layer on top of twm, but a wholly new architecture.
                                                                                                                                                                                 
 Despite this extensibility its policy is currently very minimal
 compared to most window managers--no icons, desktop backgrounds,
 sliding windows, sound effects, or whatever.
                                                                                                                                                                                 
 All high-level wm functions are implemented in Lisp for future
 extensibility or redefinition. Currently this includes menus (using
 GTK+), interactive window moving and resizing, virtual workspaces,
 iconification, focus/transient window policies, frame theme
 definitions, and many more standard window-manager functions.
                                                                                                                                                                                 
 User-configuration is possible either by writing Lisp code in a
 personal .sawmillrc file, or through the integrated customization
 system (using GTK+, see the third and fourth screenshots below).
                                                                                                                                                                                 
 A few themes are included, most mimic the window frames of particular
 Enlightenment themes (and this is where the images originated).

This looks nice.