A build note from Horizon Software, a one-person Android studio. WanderWallet is a travel budget app, and the whole thing runs on the phone: no account, no backend, no cloud. Here's how the parts that look like they need a server actually work without one.
The one constraint that shaped everything
WanderWallet has a single non-negotiable rule: it has to work with no signal. You're three countries into a trip, your phone's in airplane mode to dodge roaming charges, and you still need to know whether you're on budget. That one requirement quietly makes most of the architectural decisions for you — no login, no server round-trips, and every feature that would normally lean on a cloud API has to earn its keep another way.
The stack is deliberately boring: .NET MAUI (Android-first), CommunityToolkit.Mvvm, sqlite-net-pcl for storage, and SkiaSharp for anything I draw myself. Everything the app records lives in a local SQLite database on the device and nowhere else. "Backup" is a file you export and keep — there's no server to back up to.
The three features people assume need a backend turned out to be the most interesting to build, precisely because they don't.
