GNU ELPA - boxy

  Boxy provides an interface to create a 3D representation of
  boxes.  Each box has a relationship with one other box.  Multiple
  boxes can be related to one box.  The relationship can be any of
  the following:

  - in
  - on
  - behind
  - on top of
  - in front of
  - above
  - below
  - to the right of
  - to the left of

  The relationship determines the ordering and structure of the
  resulting boxy diagram.

  Only boxes which have their :name slot set will be drawn to the
  buffer.  Boxes without names still take up space and can have
  children, so can be used for grouping.  All diagrams have one top
  level unnamed box called a `world'.

  Each box should have either a list of markers or an action
  function.  When viewing a box that has a list of markers, the
  following keybindings are available:

  RET/mouse-1   - Jump to the first marker
  o             - Open next marker in other window.
                    Pressed multiple times, cycle through markers.
  M-RET         - Open all markers as separate buffers.
                    This will split the current window as needed.

  When viewing a box with an action function, RET and <mouse-1>
  will be bound to that function.

  Additionally, all boxes have the following keybindings defined:

  r     - Jump to the box directly related to the current box.
            Repeated presses will eventually take you to the
            top level box.
  TAB   - Cycle visibility of box's children

  See the class definition for `boxy-box' for all other available
  properties.

  To start, create an empty box named `world'.

    (let ((world (boxy-box)))

  Use the method `boxy-add-next' to add top-level boxes to the
  world, without relationships:

    (let ((cyprus (boxy-box :name "Cyprus"))
          (greece (boxy-box :name "Greece")))
      (boxy-add-next cyprus world)
      (boxy-add-next greece world)

  To ease the boxy renderer, use the :expand-siblings and
  :expand-children slots.  These should be list of functions which
  take the current box as an argument and call `boxy-add-next' to
  add sibling boxes and children boxes respectively.  Children
  boxes are defined as any box with a relationship of in, on,
  behind, in front of, or on top of.  Sibling boxes are defined as
  any box with a relationship of above, below, to the left of, or
  to the right of.

     (object-add-to-list cyprus :expand-siblings
                         '(lambda (box)
                            (boxy-add-next
                             (boxy-box :name "Lebanon" :rel "below")
                             box)))

  The expansion slots will be called when the user toggles the
  box's visibility.

  To display a box in a popup buffer, use the function `boxy-pp'.

  The methods `boxy-merge' and `boxy-merge-into' should be
  used to merge boxes together.  `boxy-merge' takes a list of
  boxes and merges them into one box.  `boxy-merge-into' takes
  two boxes and merges the first into the second.