You've heard of the Enigma cipher machine, yes? The Germans used it during WW2 for encoding and decoding messages.
If you've always wanted to play with an Enigma, the Enigma-E building kit might appeal.
The Enigma-E is a DIY Building Kit that enables you to build your own electronic variant of the famous Enigma coding machine that was used by the German army during WWII. It works just like a real Enigma and is compatible with an M3 and M4 Enigma as well as the standard Service Machines. A message encrypted on, say, a real Enigma M4 can be read on the Enigma-E and vice versa. [continue]
Link found at Slashdot.
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The Enigma coding machine
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Code-breaking the German Enigma machine