[alank2] started a class of enigma machine simulators under 10x10cm and has now announced the latest addition to this family: BinaryEnigma
This class of machines was started to take advantage of the discounted rate when ordering pcbs sized 10x10cm and under from the Far East. The original, MicroEnigma using a 2 layer board and SMT components is described here:
Another member of the family, PicoEnigma is a few millimeters smaller than MicroEnigma and uses all through hole parts, but needs a two board stack.
The smallest of the bunch, BinaryEnigma was announced in this forum post:
It appears to use an Oshpark PCB with a minimal number of components, LEDs and pushbuttons in the front and an SMT ATtiny84a in the back along with a few support components. The whole thing is powered by a CR2032 lithium battery that lasts 200 hours of machine operation.
Here are a few videos of the members of this family: