Do you know Avatars? No, not the big blue people remote-controlled by small humans. Avatars are those little (usually square) pictures that identify people in forums, blog comment threads and the like.
Do you know Gravatar? Those people had a great idea: Why should every forum administrator and blogger set up their own avatar functionality, if everything can be so easy: Just let forum users enter their email address, and have Gravatar worry about finding the right avatar for the person with this address. That way, the user just has to set up their avatar once (on gravatar.com), and it will be displayed on all their comments and postings around the internet.
Do you know Identicons? They are the answer to this question: What to do if you post a comment on a blog that uses Gravatar, but you don't have your own gravatar set up yet? It would be nice to display a picture anyway, but you haven't chosen one yet. This is where identicons come into play. When Gravatar is asked for the picture of a user it doesn't know about, it can create an random image that is guaranteed to be the same whenever the user posts somewhere. For example, this is what the identicon for the email address “email@example.com” looks like:
Do you know Unicorns? Some people say that unicorns are a magical weaponized form of ponies. Whether you agree with that or not: Unicorns are definitely awesome!
Combine all this, and you get Unicornify! It creates custom unicorn avatars in a way similar to identicons. The unicorn for the same email address as above looks like this: