Enter some text and click submit (there's a character limit of 10,000 characters). You'll get your original text, your scrambled text, and a table of character frequency back.
The substitution is very simple. There's a list of replacement characters (a-z, A-Z, 0-9, and miscellaneous punctuation characters), and each character in your text (including space) is replaced by a random character from that list.
Right now there's not much point to this, other than for my own learning. Maybe it'll some day evolve to something else.