undo-browse.el – Powerful Undo system. Back/forth/movie/redo/hilit.
In ub terminology, the undo-history is seen as a movie, each step being a frame of the movie. You can play (back/forth) the color-coded movie-history of your document, and revert your document to the frame you like. To start, type M-x ub-quick-start.
If i could save the frames and replay it later, then it could be a useful demo tool. – WilliamXu