Independent product engineering studio · Lisbon, Portugal
From design to App Store production.
Mobile and web products for agencies, startups and founders. React Native, TypeScript and AI integrations.
Two apps live on the App Store · Lead mobile engineer on a production React Native product · Payments, in-app purchases, AI features
What we do
For funded startups and scale-ups with a React Native product.
From a dedicated engineering day
For design and product agencies, and founders ready to build an app.
From one agreed scope
For products that need ongoing attention after launch.
From a monthly retainer
Selected work
Help designers analyse visual work with AI.
The client's concept and design. Kaellun built the React Native / Expo app, Firebase backend and AI analysis flow, with Apple in-app purchases, backend receipt verification, a credits ledger and real-time status updates.
Live on the App Store
EyeFirst on the App StoreSupport mindful wellbeing and self-awareness.
Rui's own product. Concept and UX design through React Native / Expo implementation, with an automated GitHub Actions CI pipeline and EAS Build/Submit delivery.
Live on the App Store
Awareness Tool on the App StoreBring creator commerce to mobile and web.
Rui / Kaellun's own platform. React Native and Next.js with Cloudflare Workers and PostgreSQL / Supabase. Mollie Connect OAuth onboarding and multi-party payment flows.
Private staging · Functional MVP
Visit Dropp.love
Keep booking leads, outreach and follow-ups in one workspace.
Rui's own React / TypeScript product. Structured leads from AI research enter through a token-authenticated API. Personalised Gmail outreach and follow-up tracking carry the work forward.
Private beta
Visit EncoreA video store for Soraya Moon. React, user accounts and Stripe payments.
Rui's artist platform. React and Cloudflare Workers, with ticketing, Stripe checkout and Printful merchandise.
Recent engagements: Pharoll (lead mobile engineering, NDA) · Collaboration with creative studio KOBU
How I work
Agree the product goal, the designs and what the release must include.
Review working software and decide the next increment together.
Test the build, prepare the release and take it through delivery.
Continue with maintenance, releases and technical sparring on a monthly retainer.
AI-native workflow (Claude Code, Codex) for speed; every change is specified, reviewed and tested by me.
For agencies
White-label mobile delivery from your Figma or Sketch designs. I implement the components, prepare the builds and join your Slack, Linear or GitHub workflow.
Your client relationship stays yours. You work directly with the engineer building the product. I've collaborated with creative studio KOBU.
Discuss an agency projectAbout
Founder & Lead Engineer
I'm the founder and lead engineer of Kaellun, based in Almada / Lisbon, Portugal. I have 3 years of commercial web and mobile delivery, including 2+ years of React Native.
My background includes a BSc in Geology at FCUL and the Academia de Código full-stack bootcamp. You work directly with me; specialists can be brought in when a project needs them.
I'm also a singer-songwriter, with 3 albums and 3 EPs.
FAQ
I work from Lisbon, with full working-day overlap with the UK and Western Europe, and four hours of overlap with US East Coast mornings.
Engagements use a company invoice. EU VAT reverse charge applies to intra-community B2B transactions where applicable. Scope and terms are agreed before work starts.
You own the code, repository and assets on payment of the invoice.
Yes. Client work under NDA is shared or published only with prior consent.
Available for new primary B2B contracts and sprints from 28 October 2026. Email me with your scope and target dates.
Contact
Send the product goal, current stage and target dates. Start with a 20-minute call.
rui@kaellun.com