One of the challenges about building apps that can work offline is syncing data between devices, servers, etc. While there are entire books written about the topics of distributed systems like this, I'll share how it works in Cook More.
Cook More is a personal digital cookbook. You can sync your grocery list and recipes with anyone else running the app, this way you can share all your recipes instantly within the app. You don't even need to have an account. This all happens over bluetooth. While I think that's a really cool feature, I really designed the sharing so that partners can have a shared grocery list without compromising their data. To that end, everything must sync seamlessly, additions, deletions, and modifications. Cook More has live-sync and a deferred-sync built in.