It took a while, but I finally managed to create my own Game Boy cartridge. With WiFi! At this point, it can only demo a simple telnet-style communication and access Wikipedia articles, but I am confident that I will showcase more in the future. For now, the interesting and surprisingly tricky part is how the thing works at all. Click the image to see the video on youtube.com. If you just want to see the cartridge in action or want to get into all the details, I highly recommend to watch the video first as it goes through the difficulties and their respective solutions. In contrast, this article here is less visual in its explanations and mostly documents the device in detail, so unless you are already familiar with the parallel memory interface of the Game Boy, you might want to start with the overview from the video.