A complete Android shopping app with no backend server at all, Firestore for data, Firebase Auth for accounts, and it syncs across devices for free.
Everything a shop needs, with no server to rent or maintain. Firestore holds the catalogue, the carts and the orders; Firebase Auth handles accounts; storage holds the images. Sign in on a second device and the cart is already there.
Built in Java with Android Studio, structured so the Firebase calls are behind a repository layer rather than scattered through the activities, which is what makes it worth reading rather than only running.
Unzip, dependencies, database, .env, first run, putting it on a real server, and a troubleshooting list for the things that actually go wrong. It is in your library beside the download, the moment you own it.
One developer, unlimited client projects. Resale of the source itself is not permitted.