After reading part of a very well-known Harry Potter fanfiction story (This Means War! - Jeconais), I was inspired to make this very simple alpha encoder which translates every character by a specified number of letters. I'm afraid I didn't build in number translating capability, though. It is obviously a very weak form of encryption, but, if you read the story, it was a great way to fool the purebloods!
The encoder is technically separate from the rest of my site. It is a hard-coded PHP script, instead of a template, so it is not straightforward to embed inline (as in, inside the text you see here.) However, you may view it here.