Hailing from Czechia, Etsy seller Extreme EDC Shop sells this unusual eXtreme Ratchet. Billed as "The smallest ratchet EDC tool in the world" (how does one verify such a thing?), the stainless steel tool is essentially a bit holder with a hexagonal hole through it, and a ratcheting mechanism hidden inside. Without the bits, they're just 5mm thick.

Here's how they work:

There are multiple versions. The smaller unit can hold two bits, and comes in both a MOLLE-compatible configuration or a keychain version. The hexagonal attachment loop on the latter is sized for a 10mm nut.

The larger of the two MOLLE-compatible units can hold four bits.

Puzzlingly, all three units appear to be the same price: About $33 without the bits, $52 with.