Nixiedoku

John Sarik's stunning Sudoku game is built around 81 vintage Nixie tubes. It uses an Arduino microcontroller board and a couple of knobs to select the digit, along with a keypad for numeric entry. There's also a video showing the beast recursively solving a puzzle - not fast or elegant, but beautiful. He's even provided all of the design files (schematics, boards, source code, and case design) in case you'd like to try your hand at building one for your evil mad scientist lair.

Nixie Sudoku [via Hack a Day]