Have you ever seen this:
41 20 6D 65 73 73 61 67 65 20 69 6E 20 68 65 78
To the untrained eye, it makes no sense. This is in fact a message hidden in hex values. This app is able to take these values and change them back into letters. Not only that, it can change your messages into those and other
types (currently binary and Base64). You can then send those messages to your friends and, if they have this or another similar app, they can see what you are saying.