Here's a cipher disk that you can print and cutout to help you manually implement the Caesar Cipher. A program to implement this cipher (and break the cipher) is available in Chapter 14 of the free programming book "Invent Your Own Computer Games with Python" at http://inventwithpython.com/chapter14.html
Simply download and printout the PDF and cut out the two circles and place them on top of each other. The key number is whichever one is opposite the outer "A" letter.
If you would like to change around the font or the logo, you can also download the original Photoshop file.