About
Felix Heller
Mobile Engineer
Frontend Engineer
About
Hi, I'm Felix — a freelance mobile and frontend developer. I shipped my first Android app while I was still in school, and more than a decade later I'm still hooked: my own apps have passed 2 million downloads, and I hold an M.Sc. in Business Informatics (GPA 1.35). Away from the keyboard you'll find me reading (books+coffee=️), at concerts, at the cinema, or on my bike.
Got a project that could use an experienced pair of hands? Let's talk — I'm always up for a new challenge.
Services
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My Skills
Programming Languages
- Kotlin
- Java
- TypeScript
- HTML
- CSS
- Dart
- GraphQL
- SQL
- JS
- PHP
- Python
Mobile Frameworks
- NativeScript
- Flutter
- ReactNative
- LibGDX
Frontend Frameworks
- Angular
- Vue.JS
- Laravel
- React.JS
Software
- AI Agent Development
- Git
- JIRA
- WordPress
- Docker
- UNIX
Principles
- Clean Code
- Software Design Patterns
- Scrum
- TDD
Works
Projects
A selection of things I've built — from personal apps with millions of downloads to client projects. Where an NDA applies, you'll find a work reference instead of a link to the final product.
Portfolio
AlcoTrack
Blood alcohol (BAC) calculator, consumption tracker, and drinking diary — all rolled into one app that helps its users keep an eye on their drinking habits.
- 250,000+ downloads
- Translated by its community into 17 languages
- 4.6 stars average rating on Google Play
- 16,000+ lines of code
DetoxDroid
Digital detox for Android: DetoxDroid strips away the attention-grabbing features of your smartphone — use your phone, rather than letting your phone use you.
- Fully open source
- 480+ stars on GitHub
- 3,000+ lines of code
CheatDroid
CheatDroid is a developer's toolbox for viewing, editing, and debugging the shared preferences and SQLite databases of Android apps.
- 2,000,000+ downloads on Google Play
- 9,000+ lines of code
M-Trust API Guard
Automated semantic versioning for Dart and Flutter packages: API Guard analyzes a package's public API, detects breaking changes, bumps the version, and writes the changelog — no more guessing whether a release is a patch or a major.
- Co-developed in a two-person team
- Open-sourced by EMD Group / Merck
- Static analysis of Dart API signatures
Own apps
SunMate
Live UV index and a personal burn time for your skin type.
SunMate
Sun protection built on the live UV index: SunMate turns the forecast into a personal burn time for your skin type — and reminds you to reapply when the real UV says so, not a fixed timer.
- UV index, burn time and vitamin D worked out on the device
- Home and lock screen widgets, UV alerts, morning briefing
- No account, no ads, no tracking
BMI Calculator
BMI, body fat and weight tracking — no ads, no tracking.
BMI Calculator
BMI, body fat and weight tracking for Android — with the metrics that go beyond BMI and real growth percentiles for children and teens.
- BRI, waist-to-height ratio and body fat on top of classic BMI
- CDC and Kromeyer-Hauschild growth references for kids
- No ads, no tracking, no account — everything stays on the device
Client work
Smart Caravan App
Companion app for GPS trackers and caravan sensor systems.
Smart Caravan App
Companion app for GPS trackers and sensor systems that lets caravan owners keep an eye on their vehicle from anywhere.
- Maintenance and bugfixing of the legacy app (NativeScript + Vue.JS)
- Ground-up development of the new Flutter app
Meeting Of Styles Website
Website and shop for an international graffiti event network.
Meeting Of Styles Website
Meeting of Styles is an international network of graffiti artists and supporters, which sponsors graffiti mural creation events in over sixteen countries. In 20 years, there have been around 400 events, featuring thousands of artists and attracting thousands of spectators.
- Re-design and development of the WordPress-based website
- Setup of the online shop
Tenant App
Whitelabel app for housing-association tenants, built from scratch.
Tenant App
From-scratch development of a whitelabel app for housing-association tenants: report damage, retrieve documents — all in the association's own branding.
- Form UIs generated dynamically from backend questionnaires
- UI development and GraphQL API integration
- Component generalization for whitelabeling
Inventory App
Lean Android app that speeds up warehouse logistics.
Inventory App
A lean Android app that speeds up warehouse logistics — built with a modern Jetpack Compose UI.
- QR code scanning for order picking
- Batch photo transfer to custom folders over corporate WiFi
E-Book & Audiobook App
E-book and audiobook lending, incl. reader and audio player.
E-Book & Audiobook App
Continued development of an Android app for borrowing, reading, and listening to e-books and audiobooks.
- Co-development of the EPUB e-reader component
- Integration of app components with server APIs
- Refinement of the app's UI
RESQSHIP Website
Website for an association for civilian sea rescue in the Mediterranean.
RESQSHIP Website
RESQSHIP is an association committed to civilian sea rescue in the Mediterranean. Its website informs about the mission and helps collect donations.
- Volunteer work (pro bono)