Projects

Things I build in public

Three things I run outside client work. They are here because claiming to build in public and then showing nothing is worse than saying nothing at all — and because what a project taught me is usually more useful to read than what it does.

Each one below includes the part that normally gets left out: the decision that turned out to matter, and the thing that went wrong before it worked.

Lieferhand

Verifizierte Lieferfahrer für Restaurants in Frankfurt, Wiesbaden, Limburg und deutschlandweit

Founder & CTO·Active · MVP phase, founded 2026

A two-sided on-demand marketplace connecting independent delivery drivers with local restaurants in Germany. Pay-per-delivery, no commission on order value, no fixed costs — designed for restaurants tired of 30 % platform fees from incumbents.

I built the backend (Spring Boot 3.4 / Java 21 on Kubernetes), Stripe Connect payouts, GDPR-compliant data flows (AGB, AVV, ID + driver-license verification), and run operations. Active in Hessen first, scaling nationwide via verified driver waitlist.

The interesting engineering is not the marketplace, it is the payouts. Stripe Connect means every driver is a payment recipient with their own onboarding, identity verification and tax status, and Germany adds requirements that most marketplace tutorials skip entirely. Getting the money to move correctly took considerably longer than getting the orders to move.

The second lesson was regulatory rather than technical. Verifying identity documents and driving licences means processing exactly the category of personal data that requires deletion concepts, processing agreements and a defensible legal basis before the first driver signs up — not afterwards. Building that in from the start cost weeks. Retrofitting it would have cost the project.

  • Spring Boot 3.4
  • Java 21
  • Kubernetes
  • Stripe Connect
  • Cloudflare
  • React Native
  • GDPR
lieferhand.de

CryptoTarget

Crypto market screener with technical indicators

Solo build·Side project · on Google Play

Mobile screener that runs RSI / MACD signals over 500+ crypto pairs in real time. Built as a React Native side project to keep my mobile and signal-processing chops sharp.

The constraint that shaped it was cost. Streaming live data for hundreds of pairs to every device is trivially easy and ruinously expensive, so the indicators are computed server-side and pushed as compact deltas rather than raw candles. That one decision is the difference between a side project and a bill.

Looking for someone to bring this kind of execution to your platform? Get in touch.