The Mac dictionary application, which you can start from Applications > Dictionary, has a secret treasure trove of reference information. Just start the Dictionary app and then in the menu bar select "Go" and then "Front/Back Matter". Once you do this, you'll get all of the additional reference information contained in the New Oxford Dictionary. Things like a complete language guide, the Declaration of Independence, the US Constitution, the history of the English language. There's all kinds of fun stuff in there. All without being online.