Open-Source Billing App Build

I’m developing a small, open-source application that makes day-to-day billing painless for service providers. At this stage I only need a clean, working MVP with a standard, simple interface and code that runs on iOS, Android, and the Web from a single shared codebase.

Core features I want in this first cut:
• Secure login for staff
• Screens to add and edit product details and customer details
• One-tap bill generation that turns the order into a PDF or printable receipt
• Automatic option to share that PDF/receipt directly to the customer’s WhatsApp chat
• Basic data storage to keep totals of sales, expenses, and outstanding creditors

I’m flexible on the tech stack as long as it is widely adopted and suits an open-source licence—Flutter, React Native, or a similar cross-platform solution would all work. Keep the UI uncluttered and intuitive so anyone can pick it up without training.

Deliver the source code in a public Git repository, along with simple setup instructions I can follow to build and run the app on all three platforms.

If this first version goes smoothly I’ll open a follow-up project for deeper reporting and analytics, so build with future extensions in mind.