Video: The TS100 is an open-source, precision soldering iron that includes the ability to program its temperature. In service of that, the device uses a tiny OLED screen, which allowed YouTube's Joric to hack the device and make playing Tetris another one of the tool's many features.
As with a lot of software hacks, this is more of a "I wonder if this is even possible?" idea as opposed to an earnest attempt to replace the Game Boy. But as pointless as it may seem, the minute-and-a-half demo video is definitely worth your time for the soundtrack alone, which finally adds lyrics to the impossibly catchy Tetris theme.