Numitron tubes are special type of displays, where digits are constructed out of segments like in 7-segment LED displays. They can be driven with standard 74HC595 shift registers. Numitron indicators require about 20mA of current so interfacing them to microcontrollers is fairly easy. Kalshagar have built really nice four Numitron digits based digital clock.
He wanted clock to be modular so that different parts could be reused in other projects if needed. To do so, he split design in to two boards – a display board which carries only tubes and driving circuit; while another part where microcontroller, RTC and backup battery is. He has done several versions of board and enclosure while eventually he stayed with rusty metal casing which looks really great.