Freelance senior mobile engineer

Mobile apps, web platforms and AI features.

Native Swift and Kotlin, React Native with Expo, edge-rendered web with Next.js and Cloudflare. Seven of my own products run live, two on the App Store, all owned end to end. Deepest experience: health data, sensors and AI in production.

Available now Remote, German or English

Shipped

Not just built. Released.

Seven products in the wild, all owned end to end.

iOS, App Store

Gearstack Health ↗

A health coach that turns sleep, HRV, training load and nutrition into one daily read. Native SwiftUI, HealthKit, Firebase, Watch app, widgets, three languages.

 iOS, App Store

CroVenture ↗

Exploration app on MapKit with proximity unlocking and a server-side anti-cheat check. Shared engine model with a Kotlin and Compose port for Android.

 Next.js, SSG

croatiaatlas.com ↗

Travel platform, five languages, 369 statically generated pages, Firestore overlay on top of a bundled seed so editors work without a deploy.
Next.js, Cloudflare Workers, D1

Gearstack Pro Dashboard

Web dashboard for coaches and clinics on top of the health app: squad overview, load and readiness per athlete, consent-based data sharing. Firestore ingestion, D1 at the edge.

Next.js, Cloudflare Workers

immobalko.com ↗

Real-estate portal for Croatia in eight languages. XML feed import from agency systems, 2,800+ live listings, image pipeline on its own CDN, rendered at the edge.

 Next.js, Cloudflare Workers

jadrivo.com ↗

Vehicle marketplace for Croatia. Dealer onboarding, XML inventory feeds, multilingual, running as a Worker at the edge.

 React, Vite

g-stack.app ↗

Product site for the health app, multilingual, with its own SEO page tree.

Gearstack Health on iPhone

August 2026 build, interface shown in German. HealthKit data condensed into readiness, AI coach, vitals, analysis and nutrition. Scrolls sideways.

Readiness view with the overall score, status and the day's contributing factors. AI coach answering a training question with a structured recommendation based on readiness. Scanning a meal from the photo library: the AI recognises the dish and its nutrients before saving. Vitals monitor with heart rate, HRV, respiration and further sensor values over time. Analysis view showing biological age and the factors behind it.

Gearstack Health on Apple Watch

A dedicated Watch app with its own target, not a mirror of the iPhone: activity, live run and heart rate zones on the wrist.

Apple Watch view showing the activity figures for the day. Apple Watch view during a run with live metrics updating. Apple Watch view showing the current heart rate zone during training.

CroVenture on iPhone

Light interface, MapKit, proximity unlocking. Same engineer, deliberately a completely different design system from Gearstack.

Overview map of Croatia with place markers for Zagreb, Rijeka, Pula, Zadar, Split and Dubrovnik plus notice cards about current travel rules. City map of Dubrovnik with a ten of 49 discovered progress bar, a list of live events and markers for places in the old town. Detail view of the Rector's Palace with a credited photo, a rating, a short description and actions for tickets, route and audio guide.

Scale, measured

Numbers from the codebase.

Counted, not estimated.

Specialisation

HealthKit, in detail.

Six production quirks, all solved.

AI in production

Core ML and LLM, live.

Everything here runs in the published app.

Also solid ground

Migration, cross-platform, grants.

Flutter removed completely

I ported a full Flutter app to native SwiftUI and then removed Flutter entirely: no engine, no pubspec, no remnants. Plenty of teams are attempting this in 2026 and few have finished it.

React Native, when it fits

Two marketplace apps built in React Native with Expo, real estate and vehicles. Native, Kotlin or React Native: the choice follows the product.

EU grant applications and compliance

Built an EU co-funded grant application for my own platform: a consortium with a medical faculty and football clubs, including budget, state-aid and MDR-scoping logic.

Swift and Kotlin in parallel

For cross-platform without Flutter or React Native: the engine logic behind Gearstack and CroVenture exists in Swift and Kotlin field for field, with shared tests asserting the same expected values.

Stack

What I work with.

iOS Swift · SwiftUI · HealthKit · Swift 6 concurrency · SwiftPM · WidgetKit · watchOS · WatchConnectivity · Combine · StoreKit 2 · Swift Testing · XCTest
AI/ML Core ML (on-device) · Gemini API · structured output · schema design · cost and latency control
Backend Firebase (Firestore, Functions, Auth, App Check) · Cloudflare Workers · D1 · Next.js
Cross-platform React Native · Expo
Android Kotlin · Jetpack Compose · Health Connect

Contact

Tell me what needs building.

And by when. I will say honestly whether it fits.

info@gearstacklabs.com →