Stefan Simić

Full-stack Product Engineer - Mobile & Web

Stefan Simić

Serbia

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Portrait of Stefan Simić

About

Building products end-to-end

Six years building web and mobile products, most recently owning a fitness platform's full stack: a React Native/Expo app, a Next.js site, Node.js services, and the internal admin behind them. Beyond the client apps, I owned subscription and paywall infrastructure, Stripe checkout, attribution, and product analytics. I'm currently expanding into cloud computing, with a focus on AWS.

Experience

Where I've shipped

  1. Head of Development - Younger Fitness

    • Led end-to-end development of the Younger fitness platform, spanning the mobile app (React Native/Expo), website (Next.js), backend services (Node.js), and internal admin dashboard.
    • Designed and delivered core product functionality across activity tracking, training experiences, onboarding, social, and gamification.
    • Built subscription and paywall infrastructure (RevenueCat), Stripe checkout flows, and affiliate and attribution integrations.
    • Drove marketing and analytics capabilities through integrations with Meta Conversions API, AppsFlyer, Klaviyo, and product analytics tools.
    • Ensured platform quality and stability through SDK upgrades, performance optimization, observability (Sentry, Clarity), and release management.
    • Built internal admin and analytics tooling supporting content management, user operations, and business insights.

  2. Software Developer - Tangled Group, Inc

    • Developed software at a company specializing in traditional and generative AI OCR, delivering ML/AI solutions optimized for IoT and resource-limited devices.
    • Worked in the Engineering and Technical department building high-performance, production-grade applications.

  3. Frontend Developer - DCLOUD

    • Implemented UIs using modern frameworks: React, Svelte, and Vue.js.
    • Created reusable, dynamic components and handled backend integration.
    • Worked with TypeScript, Tailwind CSS, Docker, Cypress (E2E), unit testing, and Agile workflows (Jira).

Skills

Tools I work with daily

Mobile

React NativeExpo (EAS)Expo RouterReanimatedNativeWind

Frontend

ReactNext.jsTypeScriptTailwind CSSReact Query

Backend & Data

Node.jsPostgreSQLSupabaseAWSREST & GraphQLMCP servers

Integrations & Observability

StripeRevenueCatSentryAppsFlyerCI/CD

Languages

How I communicate