Not actually a mode, just a quick hack for a presentation.

narrow-slides-mode.el

(defvar slide-delimiter
  "----------------------------------------------------------------------"
  "Delimiter used for changing slides")

(defun narrow-to-slide ()
  (interactive)
  (search-forward slide-delimiter)
  (next-line)
  (let ((start (point)))
    (search-forward slide-delimiter)
    (beginning-of-line)
    (previous-line)
    (narrow-to-region start (point))
    (beginning-of-buffer)
    ))

(defun enter-slide ()
  "Narrow region to this slide."
  (interactive)
  (widen)
  (next-slide)
  (previous-slide))

(defun next-slide ()
  "Narrow region to next slide."
  (interactive)
  (widen)
  (narrow-to-slide))

(defun previous-slide ()
  "Narrow region to previous slide."
  (interactive)
  (widen)
  (search-backward slide-delimiter)
  (search-backward slide-delimiter)
  (narrow-to-slide))

(global-set-key (kbd "s-e") 'widen)
(global-set-key (kbd "s-<return>") 'enter-slide)
(global-set-key (kbd "s-n") 'next-slide)
(global-set-key (kbd "s-p") 'previous-slide)