Play with the Enigma Machine, the German World War II cryptographic device broken by Alan Turing and the team at Bletchley Park, as depicted in the movie "The Imitation Game".
The number of these machines which survived the war is quite small. Recently one of these machines sold at auction for $232,000 despite being incomplete. If you have an iPad you can get this COMPLETE simulator at a discount of 99.999%
The mechanics of the machine are replicated. Pressing a key will cycle the machine and light the letter corresponding to the encoded/decoded character.
The machine can be configured fully, including selection of the three out of five rotors to be used, ring settings, and plugboard settings. In addition the machine can display rotor positions as either numbers, or letters (a feature borrowed from the naval enigmas).