Lamptron decided to launch a fan controller with a decidedly more retro look than the standard set, so it used Nixie Tubes when it made the FC10.
A Nixie tube is an electronic device used for displaying numerals or other information using glow discharge. The glass tube holds within it a wire-mesh anode and multiple cathodes, shaped like numerals or other symbols.
The orange glow discharge appears when one applies power to the cathode.
This is the technique used by the Lamptron FC10 fan controller.
The FC10 can handle four fans and displays speed in steps of 0 to 9. A 4-pin Molex connector provides the energy (up to 30W per channel).
A 5.25-inch drive bay should be enough to house this thing. Too bad the price is unknown.