Since 2017
Flutter Development
- Cross-platform mobile apps
- State management (BLoC, Riverpod)
- Platform channels & native integration
- Custom widgets & animations
- Performance optimization
Freelance since 2012
Roland Wimmer
Flutter Developer Expert & Trainer
Flutter since 2017
Android since 2010
Mobile
50+
App variants contributed to
Country, brand and platform variants
Clients
15+
Client organisations
Legacy Modernization
I analyze your existing systems and architect a migration path that minimizes risk while maximizing business continuity
Enterprise Apps
I build scalable mobile solutions using Clean Architecture, SOLID principles, and comprehensive testing strategies
Flutter & Dart Trainer
I empower your team with hands-on workshops and mentoring to ensure sustainable development practices
Technical Expertise
Specialized in building and improving enterprise-grade mobile applications with a focus on maintainability, scalability, and developer experience
Freelance since 2012
Enterprise Solutions
- Large-scale refactoring
- Legacy code modernization
- CI/CD pipeline setup
- Team mentoring & code reviews
- Architecture documentation
TDD & automation
Testing & Quality
- Test-Driven Development (TDD)
- Unit & Integration testing
- UI testing & automation
- Code coverage optimization
- Performance profiling
Since 2010
Android Native
- Kotlin & Java expertise
- MVVM & Clean Architecture
- Jetpack Compose
- Dependency Injection (Dagger/Hilt)
- Reactive programming (RxJava, Coroutines)
Featured Portfolio
Selected enterprise app development, architecture and training engagements
Scroll or swipe to explore
2027
2026
2025
2024
2023
2022
2021
2020
2019
2018
2017
2016
2015
2014
2013
2012
WOLF
WOLF Service App
2026
2026
Flutter service app with Web/PWA and native offline capability.
Implemented on-demand Web/PWA loading, drawing-cache invalidation, responsive layouts, light/dark themes and Baltic market configuration.
View WOLF Service App WOLF
MyWolf
Apr 2025 to Mar 2026
Apr 2025 to Mar 2026. Completed
Offline heating-equipment commissioning app for partners and technicians. Freelance Flutter development and architecture.
Refactored caching and Clean Architecture, improved CI, and built a multi-step golden-test framework.
View MyWolf Railsoft
Rail Soft
Dec 2023 to Jul 2024
Dec 2023 to Jul 2024. Completed
Flutter Android management app for railway operators and workshops, with wagon management, service documentation and track and wagon arrangement editing.
Built Clean Architecture, local-first offline caching and backend sync, with automated builds, crash reporting and demo distribution.
View Rail Soft Bayer
MagicScout
May 2023 to Dec 2026
May 2023 to Dec 2026. Ongoing, agreed end Dec 2026
Agricultural app supporting farmers in their day-to-day work.
Refactored a proof of concept into Clean Architecture, created modular packages and unit tests, and extended a reusable widget library.
View MagicScout
Blackned
Ridux Collaboration Client
Oct 2022 to Apr 2023
Oct 2022 to Apr 2023. Completed
Android development on the Ridux Collaboration Client.
Further project details are confidential.
View Ridux Collaboration Client Viessmann
Flutter and Dart training
Oct 2022 to Nov 2022
Oct 2022 to Nov 2022. Completed
Remote Flutter and Dart training for nine internal developers.
Covered Dart, isolates, app structure, state management, environments, animations, internationalization and desktop development.
Telekom
Vjumi
Sep 2020 to Nov 2020
Sep 2020 to Nov 2020. Completed
Base Flutter app structure and architecture for the Vjumi platform.
Handed over the app and trained the internal team in Clean Architecture, dependency injection, testing, TDD and reusable widgets.
View Vjumi MediaMarkt/Saturn
MediaMarkt/Saturn App
Jul 2019 to Mar 2022
Jul 2019 to Mar 2022. Completed
Android and iOS apps from one Flutter codebase for 11+ country variants.
Created modular architecture, a UI library, unit/integration tests and automated store delivery. Hired and mentored developers as the team grew from 3 to 10.
View MediaMarkt/Saturn App MealPro
mealPro
Oct 2018 to May 2019
Oct 2018 to May 2019. Completed
Built a B2B canteen app with Clean Architecture and white-label Android/iOS builds. Automated delivery and built a Vue.js portal for client-specific Firebase data.
Flutter developer and software architect
MediaMarktSaturn
MediaMarkt/Saturn Hybrid Apps
Aug 2018 to Jun 2020
Aug 2018 to Jun 2020. Completed
Native and hybrid development for MediaMarkt and Saturn Android and iOS apps.
Introduced Clean Architecture and a Flutter proof of concept, built native components and NFC integration, and worked on a TypeScript GraphQL service.
View MediaMarkt/Saturn Hybrid Apps REWE Group
REWE App
Nov 2017 to Jul 2018
Nov 2017 to Jul 2018. Completed
Development and maintenance of the existing REWE Android app.
Introduced Clean Architecture through a reference feature and mentored the team in architecture adoption and TDD.
View REWE App foodsharity
foodsharity
May 2017 to Apr 2018
May 2017 to Apr 2018. Completed
Led the technical concept, software design and implementation of a cross-platform Flutter app with a TypeScript backend.
Technical lead
Vodafone
Access UK
Dec 2016 to Jul 2017
Dec 2016 to Jul 2017. Completed
Employee-access solution using an Android app and AWS backend.
Designed and developed the transition from plastic access cards to SIM-based authentication.
Vodafone
Passbook SDK
Jun 2016 to Nov 2016
Jun 2016 to Nov 2016. Completed
Android library for the existing Vodafone Wallet app.
Designed and developed the Passbook SDK.
WDR
WDR app
Oct 2015 to Sep 2017
Oct 2015 to Sep 2017. Completed
Development and maintenance of the WDR Android app.
Developed app functionality, improved existing code and fixed bugs.
View WDR app Sparkasse
SparkassenScan!
May 2015 to Jun 2015
May 2015 to Jun 2015. Completed
Created an augmented-reality Android app using the metaio SDK.
Android developer
Stellantis/Opel
CarUnity
Apr 2015 to Aug 2015
Apr 2015 to Aug 2015. Completed
Developed the CarUnity Android app in a small team. Further project details are confidential.
Android developer
Huber Verlag
Tattoo-Erotica
Apr 2015 to Jun 2015
Apr 2015 to Jun 2015. Completed
Designed and developed an augmented-reality Android app for the magazine.
Android developer
Schuster Energie
Switch Box App
Dec 2014 to May 2015
Dec 2014 to May 2015. Completed
Designed and developed an Android tablet replacement for a membrane keyboard. Implemented low-level communication with proprietary electronic controls.
Android developer
grAPPfruit
A Word!
Aug 2014 to Nov 2014
Aug 2014 to Nov 2014. Completed
Designed and developed a multiplayer Unity3D game, backend game logic, client-server protocol and 3D models.
Game and backend developer
marktcom.de
Die Flohmarkt App
Feb 2014 to May 2014
Feb 2014 to May 2014. Completed
Designed and developed an Android app with REST API integration.
Android developer
View Die Flohmarkt App Die MedienPartner
Internal augmented-reality demo
Oct 2013 to Nov 2013
Oct 2013 to Nov 2013. Completed
Designed and developed an Android augmented-reality demo.
Android developer
Eli Logistics Solutions
Internal app
Oct 2013 to Nov 2013
Oct 2013 to Nov 2013. Completed
Completed an augmented-reality app and published it on Google Play.
Android developer
ADAC
ADAC Camping Guide
Nov 2012 to Nov 2013
Nov 2012 to Nov 2013. Completed
Android app for searching European camping sites.
Implemented user-data synchronization with Google Drive.
View ADAC Camping Guide
today
Interested in learning more about my approach to enterprise development?
Let's Discuss Your ProjectTrusted By Industry Leaders
I've had the privilege to work with some of Germany's most innovative companies, delivering solutions that impact millions of users
-
Global life sciences leader in healthcare & agriculture -
Europe's largest telecommunications provider -
German automotive manufacturer -
Germany's second-largest grocery retailer -
Leading European and African telecoms company -
Europe's leading consumer electronics retailer -
German savings banks network -
Europe's largest automobile club -
Heating, cooling & climate solutions -
Climate solutions & heating systems -
Germany's largest regional broadcaster (ARD member) -
High-security software solutions -
Digital railway infrastructure solutions -
Industrial automation & energy systems -
Online flea market platform - ... and many more
"Working with enterprise clients has taught me that successful digital transformation isn't just about writing code—it's about understanding business needs, mentoring teams, and building sustainable solutions that scale."— Roland Wimmer
Let's Build Something Great
Whether you need to modernize your mobile architecture, build a new Flutter app, or improve your development processes, I'm here to help
roland.wimmer@grappfruit.com
linkedin.com/in/grappfruit
GitHub
github.com/grappfruit
Medium
@roland.wimmer
Discuss a project
Ready to Transform Your Mobile Strategy?
I specialize in helping enterprises modernize their mobile applications, implement clean architecture, and build high-performance Flutter apps. Let's discuss how I can add value to your team.