Many apps say they work offline. The question that matters is where your data lives, because that decides what happens when you open the app on a plane.
| Type | Where data lives | In airplane mode | Account needed |
|---|---|---|---|
| Offline-first | On the phone | Everything works | No |
| Offline mode | On a server, cached on the phone | Viewing and queued edits only | Yes |
| Online-only | On a server | Nothing works | Yes |
An offline-first app stores every transaction on the device, so there is no account to create and no bank login to link. The trade-off is that your phone is the only copy unless you back it up yourself.
Expense Tracker: Income Manager is built offline-first for Android and iPhone. It logs an expense in three taps, splits group bills and tracks loans and EMIs, without an account.