How useful: http://www.rot13.com/ will take your text and do a simple transposition cipher (13 ahead, so ‘a’ becomes ‘n’ and ‘n’ becomes ‘a’). Perfect for spoiler discussions: people can talk about the new movie or game all they like, but unless you happen to be one of those people who can instantly transpose ciphertext in your head you have to choose to read the spoiler text. Very nice, very nice. I like it.