Full‑stack Ruby on Rails developer and tech lead with a track record of simplifying systems, improving delivery, and driving tangible business outcomes. I've led teams, modernized monoliths, integrated with complex third‑party ecosystems, and advised founders and investors — from cost efficiency and throughput to due diligence and acquisitions.
Experience
Freelancer
Tech Lead / Software Developer
Copenhagen • March 2022 - Present
Freelancing as Tech Lead for Autobutler while taking on short-term contracted development projects. Sometimes I do technical due diligence for VCs. I also build and maintain my own products.
Autobutler
Tech Lead / Software Developer
Copenhagen • April 2021 - February 2022
Full Stack lead Ruby on Rails developer, with responsibility for a small dev team and many projects including a large Ruby on Rails monolith, multiple microservices written in Ruby, Elixir & Phoenix, and an SPA React app.
- Reduced annual tech spend by 2M+ DKK via infrastructure optimization and cost discipline
- Maintained delivery velocity while rightsizing engineering from 11 → 4, enabling multi‑million DKK savings
- Systematically removed complexity, creating a codebase reliable for a small team to own and extend
- Changes had a drastic, positive impact on the bottom‑line (cost base and profitability)
ProCollective
Co-Founder & Lead Developer
Copenhagen • March 2020 - July 2022
Co‑founded and led development of a Freelance Management System used by enterprise clients. Our goal was to help companies grow using a flexible workforce.
- Shipped initial Vue SPA with Rails REST backend
- Migrated to Rails + Stimulus/Turbolinks, materially increasing delivery velocity
- Onboarded multiple clients including enterprise clients such as Publicis Groupe while active
Autobutler
Software Developer
Copenhagen • March 2019 - March 2021
Full Stack Ruby on Rails developer on multiple projects.
- Built algorithms that increased core product revenue
- Reduced complexity and automated operations; ensured reliable scaling to 1M+ users
- Delivered major systems including integrations with major insurance companies and a white‑label platform
MIX IT
Co-Founder and Lead Developer
Copenhagen • January 2019 - September 2021
Co-Founded a startup to build a fully functioning mobile ordering and POS (Point of Sale) solution which we named Adea.
- Built a browser‑based POS in Rails + AngularJS, with heavy focus on real time connections through websockets
- Launched a mobile ordering app & PWA with the Ionic Framework
- Landed initial clients; closed after assessing insufficient traction
UNOIT
Lead Software Developer
Copenhagen • February 2016 - February 2019
Led development from zero to production for a platform used by special high schools across Denmark.
- Adopted by 250+ schools for scheduling, grading, attendance, and more
- Travelled all over Denmark to host demos for, sell to, and onboard schools
- Work materially contributed to UNOIT’s acquisition by EG
UNOIT
Software Developer
Copenhagen • January 2015 - February 2016
Full‑stack Ruby on Rails and AngularJS developer. Delivered national‑scale systems monitoring the education process of 2M+ Danish citizens, with multiple integrations to Danish government systems.
Notable Experiences
Investments
I've been fortunate to participate in investments through SPVs, in some of the most interesting companies in the world:
I've also written multiple smaller checks (< 20.000 USD) for seed-stage companies, where I've invested as part of a syndicate. Most recently in a deep tech company doing satellite propulsion systems.
Advisory & Due Diligence
I've advised technical teams at multiple companies on productivity, building out their foundational architecture. One example is Mindpool (acquired). I've also performed technical due diligence for VCs.
Integrations & Technical Achievements
Selected integrations and scale highlights:
- Integrations with multiple PSPs (Stripe and Stripe Connect)
- Large integrations with legacy systems (Nets & Bankgirot for file transfer based payments)
- Customer.io & Sendgrid (1M+ SMS & emails/month with integrated customer journeys)
- Background job processing (1 billion+ jobs processed)
- OAUTH, SAML, Danish Digital ID (NemID) & other SSO
- Data warehouse enabling analysis across systems for 2M+ citizens
Other Accomplishments
- akia.io — SaaS that captures and analyzes competitors’ emails for market intel
- sammenlignkoereskoler.dk — Aggregated data and built scrapers for instructor comparison
- robinsonlistenapi.dk — Danish‑market API to check marketing protection status
- WoW & Warcraft communities — Ran large gaming community (100K+ yearly uniques) and contributed to TrinityCore
- Virtual gold farming — Built an automated operation at age 12, generating meaningful profits
Selected Results
- Autobutler — 2M+ DKK annual tech savings; 11 → 4 team with maintained velocity; drastic bottom‑line impact
- UNOIT — systems used by 250+ schools; contributed to acquisition by EG
- Mindpool — advised on product/tech; later acquired
- VC diligence — technical due diligence across early and growth‑stage deals
Skills
Languages & Frameworks
Databases
Infrastructure
Mobile
Styling
Languages
🇩🇰 Danish
Native
🇬🇧 English
Fluent
Contact
Info
Copenhagen, Denmark
Danish Nationality
Last updated: October 2025 • [email protected] • linkedin.com/in/marcuswilstrup