Not an unconventional engine, but an unconventional platform. I made the entire game on a Chromebook using the early alpha Android build of Godot. Not a great experience tbh. On top of that my game is also made for the LOWREZJAM 2023, meaning that not only did I have to stick to 2 colors and follow the theme "Light and Dark", but I also had to make the whole thing in a resolution of less than 64x64 pixels and follow one of the themes from that jam.