These single key pcbs can be used to make a dactyl based on keychron switches.
The footprints of the pcb come from the keyboard design by girish. See his blog post for more details on how to design your keyboard.
I did some tests with these pcbs, but I didn't end up building the whole keyboard. If you want to experiment with these pcbs make sure to have a hot air gun to do the SMD soldering of the IR and PT.