AliExpress-sold macropad ("Nvarcher CXT12e4 Four Knobs") with no included docs/software (at the time I purchased it 3 years ago, at least, now supported in QMK and vial).
This is the step-by-step log of identifying its firmware on a Mac and getting it working with Vial.
If you're on a linux machine, download the sources and compile I guess, I haven't tried it myself. I'll add it here when I try it.