This is a low profile wireless game controller - leverless fightstick style.

Component list:

• Adafruit Feather nRF52840 Express
• lipo battery - I used this 1200mAh one from Pimoroni
• 15x Kailh low profile choc v1 switches
• 4x M2.5x5mm screws to mount the Feather board
• 6x M3x10mm flat head (countersunk) screws to hold the case together
• some hookup wire (I used 26 AWG)

I think this lipo battery from Adafruit is the same thing as the Pimoroni one, though I'm not sure about the cable length.

Firmware: https://github.com/jfedor2/slimbox-bt

See the firmware repository for the pinout, firmware flashing instructions and general usage.