These hardware hackers managed to play the original Game Boy over an internet connection
Nintendo's Game Boy is some 30-years-old now but it is still impressive because some hardware engineers have managed to hack it and got it to play a game of Tetris against another player over an internet connection. Hardware hackers who go by stacksmashing on YouTube, have explained in a detailed video how they took the Game Boy's “native local multiplayer support using the proprietary link cable connector and tricked the aging handheld into playing a game of Tetris over the internet by making it think it was sharing a direct connection with another Game Boy”.
Besides some programming, the engineers used a Raspberry Pi connector that “fed the data sent to the link cable into a custom PC client”. Then the data was sent to a dedicated web server which then fed the data into another Game Boy.
Since the link cable interface protocol is not generic, each game will have to have the protocol adapted to get it to work with the web server, as TechCrunch pointed out. However, stacksmashing has shown that it is possible so, in theory, any Game Boy that uses a link cable for local multiplayer can be used to play online.
And that's not all from the world of retro gaming. There's a Discord channel too for interested gamers where custom boards are being planned to create better interfaces for the link cable to the Raspberry Pi, so as you don't have to cut open the cable and connect the wiring to the board manually. The guys at stacksmashing have also open-sourced their code so anyone who wants to try playing the original Dr. Mario online can give it a shot.
Most people consider old tech to be clutter but in reality, there's a lot one can salvage from it since there is “actually nothing wrong with underlying hardware". There are a whole bunch of programmers who are working on original games to run on the Game Boy console, as TechRadar states.