One engineer.
AI-augmented.
Ships fast.
Fenrir Digital is a one-man, agent-driven development studio based in Helsinki. I pair with AI to ship mobile apps, web platforms, and polished products at startup speed.
What I do
Over a decade of shipping products, from startups to enterprises like Nokia, Adidas, and Posti.
Mobile Development
I build native-quality mobile apps with React Native. Your app runs on both iOS and Android from a single codebase, without compromising on experience.
Web Applications
From complex dashboards to polished marketing sites, I build fast, accessible web apps using React and Next.js.
3D & Interactive
I create immersive 3D experiences and interactive visualizations that make your product stand out. This is what I speak about at conferences.
Product Strategy
With dual Master's degrees in Computer Science and Cognitive Science, I bring both technical and human-centered thinking to product decisions.
Companies I've worked with
From Finnish enterprises to global brands. I've helped build digital products used by millions.
Selected work
Some of the projects I'm most proud of. Each one taught me something new.
Posti Design System
Led the development of a comprehensive design system for Finland's national postal service. Built accessible, reusable components used across multiple teams.
Adidas Finders
Created interactive product finder experiences for Adidas Running, Outdoor, and Bra categories. Helped millions of customers find their perfect fit.
Apps I ship myself
Client work is half the story. These are products I design, build, and run under my own name.
I also speak at
conferences
I enjoy sharing what I've learned at React and React Native conferences around the world. My talks cover 3D graphics, cross-platform development, and making money with mobile apps.
Chain React
Portland, USA
App.js Conf
Krakow, Poland
React Native London
London, UK
React Advanced
London, UK
React Day Berlin
Berlin, Germany
The person behind
the code.
I'm Perttu Lähteenlahti, a software engineer based in Helsinki with over a decade of experience building digital products.
I hold dual Master's degrees in Computer Science and Cognitive Science from the University of Helsinki. That combination shapes how I think about building things: technically sound, but always with the user in mind.
When I'm not writing code, you'll find me speaking at conferences like Chain React and App.js Conf, or exploring the intersection of 3D graphics and mobile development.
Core skills
Perttu Lähteenlahti
Founder & Lead Developer
Helsinki, Finland
Education
M.A. Computer Science
University of Helsinki · Minor in Economics
M.A. Cognitive Science
University of Helsinki · Minor in Usability Studies
Let's build something
together.
Got a project in mind? I'd love to hear about it. Drop me an email, no strings attached.