Numpad to put aside whatever tenkeyless keyboard. I find it very usefull to choose when having or not numpad.
It is based on:

• arduino leonardo (pro micro)
• cherry mx switches
• keyboard stabilizers (screwed type)
• diodes
• wire
• keycaps
• m3 screws and nuts

arduino code for italian keyboard layout attached here:
https://github.com/mrkrafen/Numpad/blob/main/numpad_v0.ino