Here is another open source Nixie clock. It’s built with 3 boards stacked on top of each other. One for the high voltage power-supply, one for the control, and one to hold the nixies in place.
Uses an Atmega328P microcontroller with Arduino bootloader and firmware preloaded. The firmware is written in Arduino, and is fully open source. Anyone can reprogram their Nixie clock using a simple FTDI Adapter and a USB mini-b cable.