Flashcarts
Disco-Cart:
https://github.com/DiscoStarslayer/disco-cart
Based on Teensy 4.1
Also supports cartridge dumping
Cartridge and dumper in all-in-one PCB
V.Kart:
https://github.com/bmx/vkart
Dumping hardware based on MSP432
Also supports cartridge dumping
Cartridge is a simple cart with just a flash chip