ps2avrGB based number-pad sold fully assembled by YMDK on Aliexpress.
Keyboard Maintainer: QMK Community
Hardware Supported: Atmega32A
Hardware Availability: AliExpress
Make example for this keyboard (after setting up your build environment):
make ymdk_np21:default:program
Plugging the board in while pressing 'Top Left Key' (USB on top) will force it to boot bootloader without loading the firmware.
The code for NP21 is a minor edit of jj40.