Daniel Sellergren

Software Engineering Lead

• danielsellergren@gmail.com
• danielsellergren.com
• Richmond, VA, USA

Summary

Full-stack engineering leader with 15+ years experience building modern, sustainable web applications. I enjoy working on infrastructure and back-end applications, pure JavaScript and its frameworks, as well as accessible and semantic HTML and CSS. I am a cultural keystone who loves building empathetic and resilient teams, mentoring junior developers, speaking to groups on interesting topics, and explaining technical topics to non-technical people. Outside of engineering I take joy in my work with non-profits, landscape photography, event planning, gardening, and running long distances.

Key Skills

• Ruby, Ruby on Rails
• JavaScript, Node, React, React Native, HTML, CSS
• PostgreSQL, MongoDB, MySQL
• Redis, Sidekiq, Kafka
• Docker, Kubernetes
• AWS, Fly, Heroku
• macOS, Linux
• Git, GitHub, GitLab
• Team management, automation-as-documentation, asynchronous communication
• Artificial intelligence, machine learning, signal processing

Professional Experience

Senior Software Engineer - ProTrainings (2025-present)

• Spearheaded major modernization effort for legacy codebase, helping build out test suite and assisting with platform upgrades from Rails 5.x to modern versions. Additionally took a lead role in modernizing and optimizing both code and processes.
• Built a v2 of an internal-facing and external-facing API using OAuth2 and modern best practices.
• Moved dozens of existing tracker and analytics services to Google Tag Manager.

Head of Engineering - GenStudios (2023-2024)

• Developed MVP for financial instrument trading social network, launching to an initial waitlist of over 10,000 users.
• Engineered serverless code-to-video generation, using ffmpeg and Remotion.
• Designed and built system architecture to scale to millions of transactions, using AWS CDK and Terraform.
• Managed multiple international remote teams (Poland, Ukraine, Brazil, US) working on mobile, web, and backend transaction processing.

Senior Software Engineer & Engineering Manager - Hopin (2020-2022)

• Early stage engineer helping grow the company from 13 to 1,200 people over two years.
• Handled new feature work and maintenance for a Rails monolith and React frontend, servicing millions of users.
• Responsible for complete overhaul of self-service Payments system as well as migration of thousands of subscriptions from Stripe to Chargebee.
• Built and maintained over 30 internal tools and dashboards from the ground up to fill various needs across Support, Finance, Engineering, and Sales.
• Created a set of Ruby microservices for Content Moderation which leveraged Kubernetes, Gitlab CI, Kafka, AWS SQS and Lambdas, as well as integration with two third-party providers to handle hundreds of thousands of messages per week.
• Founding engineering presenter at the Hopin Academy, our onboarding process for all new hires from Engineering to Sales to Executive Leadership.
• Founder and host of the Engineering All Hands internal showcase.

Platform Developer - Mobelux (2016-2020)

• Built multiple large Rails applications from scratch, including a local produce delivery service, a custom multi-tenant CMS servicing over a dozen clients, and internal tooling.
• Oversaw every Ruby project: managing junior developers, answering questions, reviewing code, merging pull requests, and deploying applications to multiple environments.
• Led major upgrade efforts, moving Rails projects from as early as 2.3 to modern versions.
• Contributed significantly on a wide range of technologies and frameworks from Python/Django to React Native to custom in-store displays.
• Regularly interfaced with clients at kickoff meetings, sprint planning, and on-site visits.
• Volunteered in the community by leading and presenting at developer meetups, as well as programming and robotics events for local children.

Full Stack Developer - INM United (2011-2016)

• Built dozens of websites and applications, from one-page brochure sites as a front-end developer to full-stack web applications for international companies in Ruby, PHP, and .NET.
• Traveled to embedded on-site development sprints, working regularly with clients, executives, and in-house development teams.

Education

University of Miami (2002-2006)

• B.S. Neuroscience, Minor in Biology
• B.A. Film Production, Minor in Philosophy

Virginia Commonwealth University (2011-2014)

• M.S. Computer Science
• Emphasis on AI/ML, signal processing, and brain-computer interfaces.

Community

• Fundraiser and member of the Board of Directors for Safe Harbor, providing services to survivors of human trafficking and domestic violence. (2018-2025)
• Cofounder and regular speaker at ReactJS(RVA). (2018-2020)
• Author of activeadmin-history and css_naked_day_rails gems.
• Spanish speaker (~A2, Conversational).