There are 2 repositories under commodore-16 topic.
Sidekick64: A Versatile Software-Defined Cartridge for the C64, C128, C16, plus/4, and VIC20
Commodore 16 schematics and PCB, redrawn in Kicad
Open Hardware 8/16/32 Kb Cartridge for the Commodore 16, 116 and Plus/4
Simple Console 6502/C64 Emulator written in C++ for Portability (ported from simple-emu-c64) ***AND see branches for embedded, LCD versions
Open Hardware 64 Kb RAM Expansion for the Commodore 16
Open Hardware Joystick Adapter for C-16, C-116 and Plus/4
C16/+4 Version of the WiC64 WiFi Adapter
1984 Commodore shoot-em-up Xzap, recreated in Godot.
Parallel Port Adapter for the Commodore Plus/4
RS-232 Serial Port Adapter for the Commodore Plus/4
4-player joystick adapter for the Commodore 16, 116 and Plus/4 with 2-button support
A versatile bench power supply unit that can power Commodore retrocomputers
Tapuino from http://www.sweetlilmre.com and a 3D printable enclosure
8-player joystick adapter for the Commodore 16, 116 and Plus/4