Projects I've Built

Table of Contents

Intro

From building EV charging infrastructure used by tens of thousands of drivers across Europe to co-founding an AI-powered mental well-being startup, here are the highlights of what I’ve shipped and why they matter.

Eudaimo Labs (Co-founder)

Timeframe: 2022-2025

Co-founded an AI-powered mental well-being startup. Shaped product vision, built MVPs end-to-end, and headed all engineering efforts alongside two business co-founders.

Unable to achieve product-market fit despite multiple pivots, we decided to wind down operations in 2025.

1. Mental Well-Being App (Original Concept)

   • Drafted features and gathered content to personalize user experience.
   • Tech: Figma, Notion.

2. Stress Management Chatbot (First Pivot)

   • Launched a Telegram bot in a few weeks to assess user goals and deliver tailored stress tips.
   • Integrated OpenAI’s GPT-3.5 (pre-SDK) to deliver personalized stress insights to alpha users.
   • Tech: TypeScript, Redis, OpenAI (GPT-3.5), Hetzner.

3. Argo : Organizational Health Agent (Second Pivot)

   • Built a Slack bot that analyzes team messages to surface misalignment and sentiment.
   • Developed data pipeline that helped teams identify communication breakdowns before they escalated.
   • Tech: Go, Postgres, OpenAI (GPT-4), Python, Matplotlib, Hetzner.

Client Work

Between 2021 and 2024 I occasionally worked on projects for clients.

• Tina

  MVP: Built an AI-driven recruitment funnel to auto-qualify candidates using WhatsApp.

  Outcome: Reduced manual screening time.

  Tech: TypeScript, Supabase, OpenAI (GPT-4o), fly.io.

• Novolto (Smart Water Heater)

  Novolto builds smart water heaters optimized for solar energy usage.

  • PoC (2023). Architected and built a system integrating real-time solar feed-in data to optimize energy costs.

    Outcome: Enabled the first tests with hardware.

    Tech: Go, RabbitMQ, SQLite, Hetzner.

  • Scale-up (2024). Optimized performance and added monitoring.

    Outcome: Scaled from tens to hundreds of devices.

    Tech: Python, FastAPI, Supabase, Next.js, render.com.

• COMo Berlin

  Developed UI for an open source CO₂ sensor platform that helps public spaces and offices monitor air quality via LoRaWAN.

  Outcome: Multiple installations across Berlin, contributing to public health monitoring.

  Tech: Vue 3, Chart.js, Tailwind, Django.

ubitricity (Senior Software Engineer)

I started my career at ubitricity in 2013 and worked there until 2020, then rejoined part-time (2023-2024) while co-founding Eudaimo Labs.

ubitricity builds public EV charging infrastructure.

• Firmware Rewrite

  Transitioned development in-house and rewrote the entire firmware with a five-person team.

  Outcome: Faster feature development and a more robust product.

  Tech: Java, Android (AOSP).

• Scan and Charge

  Built a full-stack EV charging solution allowing users to initiate charging sessions by scanning a code.

  Outcome: Enabled strategic company pivot leading to 8-figure acquisition by Shell.

  Tech: Python, Flask, SQLite, jQuery.

• Local Load Leveling

  Developed a dynamic local load-management system for car-parks. Allowing facility managers to balance EV charging beyond grid capacity.

  Outcome: Opened new markets for the company.

  Tech: Java, Spring, WebSockets.

borg (Full-Stack Software Engineer)

Timeframe: 2021-2022

borg built hive.one (now defunct), a platform that mapped and ranked online communities by identifying influential Twitter accounts (similar to how Google ranks websites).

• Led rewrite of the frontend of hive.one during major redesign.

  Outcome: Faster feature development and a more modern UI.

  Tech: Next.js, Styled Components, Sentry, D3.

• Implemented “interests” feature end-to-end. Allowing users to find and follow different communities on Twitter.

  Outcome: Increased user engagement and signups.

  Tech: Next.js, Express.js, TypeORM, AWS (EC2, RDS, S3).

Side Projects

Here are some recent side projects.

• Tango Video Search ( open source )

  Fast, AI-powered index for finding Tango performances by dancer or orchestra. Indexed over 20M tokens worth of YouTube metadata for sub-second search.

  Tech: TypeScript, React Router, Radix Themes, SQLite, Drizzle ORM, fly.io.

• tldw ( open source )

  CLI tool that summarizes YouTube podcast transcripts into concise notes. Includes an MCP server for AI assistant integration.

  Tech: Go, cobra, yt-dlp, mcp-go, openai-go.

• Web Push Notifications PoC ( open source )

  Simple proof-of-concept for web push notifications in a Next.js PWA.

  Tech: Next.js, Web Push API, Upstash Redis.

• christianrotzoll.com

  This very website.

  Tech: Hugo, CSS, Markdown.

• Tango Card Game

  Designed and prototyped an original Tango-themed card game.

  Friends who play-tested it say “it’s actually fun to play”.

  Tech: blank playing cards, printable label paper, cutter.