Billin - Fast invoice maker with ease

Create, send, and track professional invoices in seconds. Billin helps freelancers and small businesses get paid faster, stay organized, and keep accounting stress-free.

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Inspiration

Freelancers and small business owners often waste time managing spreadsheets, receipts, and outdated invoicing tools. We wanted to build something simple, fast, and mobile-first that removes the stress from billing while helping professionals look polished and get paid on time.

What it does

Billin is a smart invoice maker that allows users to:

  • Create invoices in seconds.
  • Add taxes, discounts, and services with auto-calculations.
  • Send invoices via email or share via the native OS mechanism.
  • Track payments, overdue bills, and balances.

How we built it

We built Billin using Kotlin Multiplatform and Compose Multiplatform to create a seamless experience across Android and iOS. The backend is powered by a secure cloud service with encrypted data storage and sync written in Kotlin/Spring. We focused heavily on UI/UX to keep the workflow minimal and intuitive, while still offering professional features like PDF export, reports, and client management.

Challenges we ran into

  • Designing a clean, professional UI while keeping the process extremely simple.
  • Handling multiple currencies, tax rates, and discounts in a way that feels natural.
  • Building a secure storage and backup system that protects sensitive business data.
  • Ensuring smooth PDF generation and reliable sharing from mobile devices.

Accomplishments that we're proud of

  • Launched a fully working invoicing app that is already helping freelancers save time.
  • Implemented a simple but powerful accounting flow that doesn’t overwhelm non-experts.
  • Built a production-ready design system using Compose Multiplatform, making the app both beautiful and scalable across iOS and Android using a single codebase.
  • Received positive early feedback from users about speed, simplicity, and design.

What we learned

  • The importance of balancing power vs. simplicity: users want features, but they also want speed.
  • How Kotlin Multiplatform and Compose Multiplatform can accelerate development while keeping code clean and reusable.
  • The value of user testing early – small feedback loops saved us from over-complicating the design.

What’s next for Billin

  • Adding more multi-platform support (Web & potentially Desktop via Compose Multiplatform).
  • Expanding reporting & analytics features for small businesses.
  • Integrating payment gateways so clients can pay invoices instantly.
  • Growing our community of freelancers and small businesses worldwide.

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