Programming problem:

UNDO REDO
Build a simple undo/redo system in any object-oriented programming
language. It should meet these criteria:
      * An unlimited number of operations can be performed, undone and
        redone
      * The system is generic and can easily be extended with new
        kinds of actions
      * The code is production quality
      * The undo/redo functionality is demonstrated in a simple
        console application
      * It doesn't use heavily platform-specific code