Here is a very neat project:
Match 4The game is a simple recreation of the tabletop game Connect 4, but the first game (that I'm aware of) that supports cross-platform play -- between Genesis consoles and various GameBoy models (DMG/Color/Advance), via a custom link cable
The site doesn't mention if it supports play between two separate Genesis consoles "Zero Tolerance"-style (will update if I get an answer from the dev) confirmed it does Gen-Gen play.
https://kyuchumimo.itch.io/match-4
