About
Engineer by training. Product builder by obsession.
I'm Relja, a graduated software engineer and iOS full-stack developer from Belgrade, Serbia. While most kids were playing video games, I was learning how to build them. At 16 I was already writing Swift alongside senior developers from major tech companies, taking on real-world tasks just to sharpen my skills, because for me coding was never just work.
From there I went on to study software engineering at university, where the coursework came easily because I was already building the real thing every day. So instead of waiting for a diploma to start, I launched both careers in parallel: a freelance practice serving clients around the world, and my own solopreneur path shipping products under my name. Both are still going strong today, and feed each other constantly.
But I'm not just a developer for hire, I'm a founder. I have 12 apps live on the App Store, used by more than 4,000 people, AirPosture alone has over 2,000 users and spans iPhone, Apple Watch and macOS: AI-powered wellness and style apps, voice-first study tools, fintech with real bank connections, products with paying subscribers that I design, build, launch and market myself. Every startup of mine is a lab where I learn what actually makes apps succeed: positioning, App Store optimization, paywalls that convert, retention that lasts. And that founder experience is exactly what my clients get: I think about your users, your conversion and your launch the way I think about my own.
I work the way small, excellent teams work, except the team is one person. SwiftUI and modern Swift on the front, Firebase, Supabase or custom Python backends behind it, RevenueCat and StoreKit 2 for monetization, a design sensibility shaped by Apple's own products, and a modern AI-accelerated toolchain that lets one person ship at team speed.
A big part of my work lives in health-tech and life sciences: posture tracking on real motion sensors, GLP-1 nutrition, AI skin analysis, HealthKit-driven energy coaching, and Lab+, an experimental-design validation platform for researchers. It's a domain where my security-first engineering and respect for sensitive user data matter as much as the code.
On Upwork I'm Top Rated with a 100% Job Success score, and every client review I've ever received is five stars. I take on a small number of projects at a time and treat each one like my own product.
Away from the keyboard you'll find me playing guitar, in the gym, or on a tennis court. And in true Serbian tradition, I craft homemade rakija passed down through generations of my family, like shipping good software, it's all about precision, patience and caring how the result feels when you share it.
Relja Bulajić
Belgrade, Serbia
Belgrade ↔ New York
Most of my clients are US-based; I work on their time zone when it matters.
Where it started
Long before the App Store, I was building, inventing and competing. The instinct came first; the craft caught up later.
An award-winning Arduino sensor, at 17.
In high school I designed an Arduino-based sensor system to repel moles from rural farmland using ground vibration, and won an award for the idea at a national Arduino competition. It was my first real invention: a complete hardware concept, not a class assignment. I couldn't take it to production at the time because the sensor hardware was beyond what a teenager could fund, but the lesson stuck. Turning a real-world problem into a working system is still exactly what I do, just in software now.
Student of the Generation
Graduated top of my high-school generation, the single highest distinction the school awards.
1st place · Python
Won a local programming competition in Python during high school, my first taste of building under pressure.
Arduino · certified
Completed a formal Arduino course and certification, where the hardware-meets-software bug first bit.
How I work
Ownership, end to end
I don't hand off problems. Design, architecture, code, App Store review, one person accountable for the whole journey, from first sketch to published app.
Apple-grade polish
Pixel-perfect SwiftUI, native motion, attention to the details users feel but never name. If it wouldn't pass for a first-party app, it isn't done.
Speed without debt
Fast iterations on clean MVVM architecture, most apps go from idea to TestFlight in weeks, built on foundations that survive version 2, 3 and 10.
Founder mindset
I build and launch my own startups, so I treat your product like one of mine: questioning scope, protecting the user experience, and caring about what happens after launch, not just the handover.
Trust by default
Clear communication, realistic milestones, honest trade-offs. My clients' reviews say it better than I can, every single one is 5.0.
The stack, in detail
Grounded in shipped products, not tutorials, every framework below is running in production right now.
Swift & SwiftUI
iOS CoreMy native language. Clean, modular MVVM with the Observation framework and Swift Concurrency, interfaces with first-party polish, built to survive v2, v3 and v10.
Apple Ecosystem
System FrameworksThe deep integrations that make an app feel like part of the OS, health, motion, screen time, weather, Siri, Live Activities, widgets and the Watch. This is where most iOS developers stop; it's where my apps start.
AI Engineering
OpenAI · GeminiProduction AI features, not demos: vision models that recognize food and garments from a photo, voice answers graded by AI, coaching engines grounded in the user's own data, with cost-tiered model routing (4o for depth, 4o-mini for scale).
Firebase
Realtime BackendMy default for realtime products, auth flows, live data sync, server logic and push, hardened with App Check and security rules that have passed real App Store scrutiny.
Supabase & Postgres
Relational BackendPostgres power with a modern developer experience. My choice when an app needs relational data, row-level security and clean typed APIs from Swift.
Python & FastAPI
Custom BackendsWhen an app needs its own brain, I build it: FastAPI services over PostgreSQL with Alembic migrations, structured logging and a pytest suite held above 80% coverage, fintech-grade discipline.
Fintech & Monetization
PaymentsReal money flows: Plaid bank connections, Stripe payments, StoreKit 2 subscriptions and RevenueCat paywalls, plus the App Store review process most developers fear, handled on every launch.
Security & DevOps
Hardened by defaultEvery release ships through a security audit: hardened auth flows, strict Firestore and row-level security rules, App Check, encrypted local storage and secrets that never touch git. Plus the server administration and DevOps to keep production infrastructure locked down. Zero security incidents across every app I have shipped.
Web & Full-Stack
Next.js · ReactLanding pages, dashboards and web companions for my apps, modern React on Vercel. This site is one of them.
Craft & Tooling
How it shipsDesigned in Figma, profiled in Instruments, monitored with Sentry, shipped through TestFlight. I run an AI-accelerated workflow (Claude Code, Codex) the way senior engineers run CI: it multiplies my speed, while architecture, review and judgment stay mine.