There is the MegaWiFi (https://github.com/doragasu/mw https://github.com/doragasu/mw), an ESP8266-enabled Sega Genesis cart which exists as a open source hardwa

There is the MegaWiFi (https://github.com/doragasu/mw https://github.com/doragasu/mw), an ESP8266-enabled Sega Genesis cart which exists as a open source hardware specification but not a commercial product. You could put one of these together from the spec and then write an online game for the Genesis.