Projects I've Built

Table of Contents

Intro

From EV charging infrastructure used by tens of thousands of drivers across Europe to voice agents and AI features at Superchat. Here’s what I’ve built.

Superchat (Software Engineer)

Timeframe: 2025 – present

Superchat is a multi-channel messaging platform. It consolidates WhatsApp, Instagram, email, SMS, and more into a single inbox for businesses.

• AI Calling

  Built a voice agent handling inbound calls, retrieving knowledge, and taking action on behalf of businesses.

  Outcome: Extended the platform beyond chat into calling.

  Tech: Kotlin, Python, LiveKit, AWS

• AI Agent Migration

  Migrated the platform’s AI agents to a new internal LangGraph-based stack.

  Outcome: Faster iteration on AI features.

  Tech: Kotlin, Python, LangGraph, AWS

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 start charging sessions by scanning a QR code.

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

  Tech: Python, Flask, SQLite, jQuery

• Local Load Balancing

  Developed a dynamic local load-management system for underground parking garages. 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

• rascal ( open source )

  Runs coding agents remotely on your own server. Point it at a GitHub issue and it ships a PR. Supports Claude Code and Codex as agent runtimes.

  Tech: Go, Hetzner

• 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