Retro puzzle maker is a toy I made back in December of 2018 – it allows you to create a short 8-level puzzle game for the NES, and download a rom of it.
The thing that’s kind of interesting is, the editor runs entirely on the Nintendo NES – it can be run on the site with an emulator, or run on your console. (If run on the console, it will generate a QR code that can be uploaded to the site to get your rom download!)