EDIT: The normals of mtg-star were flipped inwards. Should print correctly now. I've also made a cleaner version of mtg-number2.stl with less janky geometry (and much tighter tolerances, since 3D printers have come a long way since back when I published this)

EDIT: updated number wheel with the solution by Vano7750/Ivan Sitas for a better overflow handling. Just use mtg-number-V2.stl instead of mtg-number.stl

Here's a video of it in action

The ten's digit automatically rolls over thanks to an embedded geneva wheel, courtesy of jessed. (Parameterized gears by LeemonBaird.) (yay public domain!)

The original purpose of this was as a life counter for Magic: the Gathering. It's scaled in just the right way that it would fit into the lower half of an MtG card.
Depending on the tolerances you get out of your printer, you may want to scale it up. If your printer is well-calibrated, you should be able to get it assembled with minimal sanding even at a 80% scale.

How to print

Just print all STLs except the spring.stl and mtg-number.stl.

The spring part makes the wheel snap much more, but makes the whole thing harder to turn. Print it if you need / prefer.

You'll need some superglue to glue the ten's digit plate to its base. It's designed with a very loose fit, to allow gluing it in just the right orientation.

The mechanism was designed in OpenScad by my flatmate, the enclosure was made in blender.