A 100% offline family budget app, designed for the CFA franc zone.
01
Context
Mbongo (formerly MonBudget) is a family budgeting and micro-accounting app, 100% offline, built for the CFA franc zone (CEMAC and UEMOA).
It is not yet published on Google Play.
02
Ground constraints
Cash and Mobile Money dominate, and recurring subscriptions are rejected. The core of the app is therefore free and private, and it works without Internet: the manifest declares no Internet permission.
03
Exact arithmetic
All amounts are 64-bit integers (long) expressed in CFA francs. No float or double type is used: arithmetic stays exact, with no rounding errors.
04
Architecture
Android in Java 17 with Jetpack: Room (relational SQLite) for the Category, Budget, Expense and Income entities, ViewModel, LiveData and the Navigation Component. The interface follows Material 3, charts use MPAndroidChart and WindowManager adapts the layout to tablets and foldables.
Database access goes through asynchronous execution (AppExecutors).
05
Key features
Quick entry in 3 seconds, monthly budget envelopes, charts (breakdown, six-month bars, day of the week), market-receipt splitting into sub-items and a reallocation assistant between envelopes when a budget is exceeded.
CSV exports, JSON backups, monthly PDF reports, a one-tap home-screen widget, PIN or biometric lock (PBKDF2 / SHA-256 encryption) and an accessibility audit (TalkBack).
06
Results
A 3.0 MB APK (4.5 MB as an AAB) with no Internet permission. 28 development phases are complete, validated with unit tests and on a physical tablet.