The brief.
Most finance apps either gamify your money or treat you like a balance sheet. CashZen is for everyone in between: people who want to understand their money without thinking about it constantly. The product had to be calm, fast, and almost boring — in the way a good notebook is boring.
Bills as a graph.
Every recurring obligation — rent, electricity, streaming, the gym membership you forgot — is a node in a small graph with a cadence and a relationship to your income. I model that explicitly so the app can answer the question that actually matters: can I afford the next two weeks? Without ever showing you a chart you didn't ask for.
Mobile-first, paranoid by default.
The Android app is the canonical surface. I use a native shell for secure sessions and biometric unlock, and I encrypt sensitive fields client-side before they ever reach the database. Row-level isolation ensures that, even with my own credentials, I cannot read your ledger. That is the whole point.
Production-grade payment logic.
It is shockingly easy to write a "bill reminder" feature that double-pays or silently misses a month. I treat the bill scheduler as the most important code I own: idempotent state transitions, a deterministic clock, and an event log that explains, in plain Vietnamese or English, what happened and why.
What I am proud of.
The first time a beta user said "I forgot the app exists, but I haven't been late in three months" — that's the success metric. CashZen aspires to be invisible in the best way: a small piece of software that gives you back the mental tax of money.