On Emacs: http://www.emacswiki.org/emacs/FullScreen

On a Mac, with Aquamacs:

  (defun writeroom ()
  "Switches to a WriteRoom-like fullscreen style"
  (interactive)	
  (when (featurep 'aquamacs) 
    (color-theme-initialize)
    (color-theme-charcoal-black)
    (aquamacs-autoface-mode 0)
    (aquamacs-toggle-full-frame)
    (scroll-bar-mode -1)))

And then do

  Alt-x writeroom