Stefan Simić

Full-Stack Software Engineer with 6+ years of experience building web and mobile products. Most recently owned the end-to-end architecture for a fitness platform including a React Native/Expo mobile app, Next.js web applications, Node.js microservices, and internal admin tools. Proven track record in sub/paywall architecture, Stripe integrations, attribution, and analytics. Currently expanding cloud expertise with a focus on AWS.

1. Head of Development - Younger Fitness

   Oct 2024 – Aug 2026

   • 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

   Apr 2022 – Feb 2024

   • 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

   Jun 2020 – Apr 2022

   • 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).