Tchona

Tchona ("look" in Kabiye, the language of my ethnic group in Togo) is an offline-first phone app for small traders: market sellers, shopkeepers, street vendors, wholesalers and food makers. It turns everyday entries (products, sales, expenses, credit given to clients) into figures a vendor rarely gets to see: turnover by day, week and month, margin per product, a month-end projection, and the point where sales stop covering fixed costs. A "what if" simulator lets them test a price change or a different sales pace before committing to it. Everything runs on the phone with no account and no network; data is backed up as an encrypted file shared over WhatsApp. It started as a personal project to help one market vendor and is now used by two.

The problem

A vendor sets a price on each item but never gets to a clear picture of what those prices produce. Over a day or a month, what is the actual turnover? Which products carry the margin? Would raising one price, or selling a bit more each day, change anything? Without doing the arithmetic by hand there is no answer, so pricing and stock decisions are made on feel.

The approach

I modelled the vendor's day as a few simple objects (products with a computed cost of goods, sales, expenses, client credit) and built every figure on top of them, on the device: turnover by period, margin per product, a weighted moving average forecast, days before a product runs out. The interface asks one question per screen in plain language, with large buttons and a number pad, so recording a sale takes a few taps. The app is a Vue 3 PWA with Dexie (IndexedDB) as the source of truth; it installs from a WhatsApp link, works fully offline, and backs up to an encrypted file the vendor sends to themselves or a trusted contact.

The result

• A vendor now sees turnover by day, week and month, margin per product and a month-end projection, without doing any calculation.
• The simulator answers the recurring question, "what if I change this price or sell more," with a concrete profit figure before the decision is made.
• Two vendors use it day to day, mainly for the projections.
• Runs fully offline and installs from a WhatsApp link; in production at tchona.vercel.app.

Key features

• Quick sale entry: one question per screen (product, quantity, price, paid or on credit), a few taps to record.
• Automatic cost of goods and margin: enter what you paid, the app computes unit cost, margin and a suggested selling price.
• Turnover and profit by day, week and month, with top products and a list of unpaid client credit by name.
• Forecasts: month-end turnover from a weighted moving average, and days before each product runs out of stock.
• "What if" simulator: test a price change, a daily sales pace or an expense change and read the projected profit against the current one.
• Stock tracking with a low-stock alert threshold per product; expenses, recurring expenses and monthly budget caps per category.
• Commissions for people who pay a cut on sales: percentage, fixed, per unit, tiered or mixed, on total turnover, one product or profit.
• Works offline; encrypted file backup shared over WhatsApp or to a trusted contact; optional PIN lock.