I have been wanting to make an Enigma Simulator with 16 segment displays, leds and buttons, but the Arduino Nano/Uno do not have sufficient I/O pins to do that. The Mega2560 R3 Pro Mini changes all that. It has enough IO pins to drive all the LEDs, read all the keys and have a full 26 letter plugboard without resorting to crazy multiplexing tricks. Below is an image of the board.
To read more, follow this hackaday io project here: