Replaces certain letters with others to give a language a more fantasy-esque sound. The reversed alphabet options are closer to gibberish, but might be useful for some things.
I make no guarantees as to what will happen if you put funny ASCII characters in the text box. I might have gotten the Xanth translation wrong way 'round - someone who has the books closer to hand than I do, let me know.
The custom option lets you put in your own alternate alphabet. Just remember to write it down somewhere if you plan on using it again, since it won't save if you change alphabets. The random option is not completely random - rather, it chooses randomly among the other alternate alphabets.