[brewski]

For linux environments, instead of darkroom-mode you can put this in your .emacs file to toggle fullscreen:

  ;;; Fullscreen
  (defun switch-full-screen ()
    (interactive)
    (shell-command "wmctrl -r :ACTIVE: -btoggle,fullscreen"))

  (global-set-key (kbd "<f12>") 'switch-full-screen)

[wallrat]

Alternative if you don't have wmctrl installed (not default in Ubuntu for example):

  ;; Fullscreen
  (defun switch-full-screen ()
    (interactive)
    (x-send-client-message nil 0 nil "_NET_WM_STATE" 32
                           '(2 "_NET_WM_STATE_FULLSCREEN" 0)))

[eru]

You can also start using xmonad.

[mziulu]

Another alternative that, AFAICS, doesn't use anything external to emacs

    ;;; Full-screen mode
   (defun toggle-max-window ()
      (interactive)
      (set-frame-parameter nil 'fullscreen
                       (if (frame-parameter nil 'fullscreen)
                           nil
                         'fullboth)))
   (global-set-key (kbd "<C-M-return>") 'toggle-max-window)

[sambeau]

or

  sudo apt-get install emacs23-nox

;-)