Interesting image from the Big Bang Fair. This was built by GCHQ. This is what the card at the back says:
The Raspberry Pi Demo
The cluster is currently running a historically accurate, distributed Bletchley Bombe, capable of deciphering several flavours of Enigma encoded messages. In addition, individual nodes can function as historically accurate Enigma devices, to Army (3 wheel) or Naval (4 wheel) specifications.