Arcadinator consists of a breakout board and a dual joystick/gamepad usb composite firmware.
The breakout board is designed for an STM32F103 Bluepill, an NRF24L01 Board and 26 JST XH connectors.

Arcadinator is meant to be a cheap and open alternative for arcade control panel-to-usb boards like "zero delay".
Additionally, Arcadinator supports two players and you can optionally use it wirelessly via NRF24L01.

I designed the breakout board with an Altium License from work,
but I will try to design the next iteration with Kicad.
There is also an import of the files on https://oshwlab.com/retrobeefhw/arcadinatorv1,
a backup of the import here and you can find the gerber files I sent to JLCPCB here

The firmware is still work in progress, but enumeration as dual gamepad usb composite device and hid reports on button presses already work. I also started porting NRF24 code from STM32 HAL to libopencm3.
Before I decided to use libopencm3, I experimented with stm32duino,
but could not get a joystick composite device to work quickly.
You can find a working wireless keyboard experiment here

libopencm3 prerequisites
OpenOCD

git clone --recursive https://github.com/RetroBeef/ArcadinatorV1
cd ArcadinatorV1/firmware
make -C libopencm3 #you need to do this only once
make flash

The hardware is licensed under CERN Open Hardware Licence Version 2 - Strongly Reciprocal
and the firmware is licensed under GNU GENERAL PUBLIC LICENSE Version 3