My favorite:

Let's look at a typical novice's session with the mighty ed:

  golem> ed

  ?
  help
  ?
  ?
  ?
  quit
  ?
  exit
  ?
  bye
  ?
  hello? 
  ?
  eat flaming death
  ?
  ^C
  ?
  ^C
  ?
  ^D
  ?

  ---
  Note the consistent user interface and error reportage.  Ed is
  generous enough to flag errors, yet prudent enough not to overwhelm
  the novice with verbosity.