A fast, open-source, Redis-compatible in-memory key-value store and database, written from scratch in Go. It speaks the same protocol as Redis, so redis-cli and existing client libraries work with it out of the box. It supports pub/sub, transactions with optimistic locking, and append-only file (AOF) persistence that recovers cleanly even if the server crashes mid-transaction. It's backed by 55 tests and serves about 41k GET requests a second.

An AI study platform that turns any topic into video lessons, notes, mind maps and quizzes, with payments, rate limiting and caching built in.

An AI hairstyle try-on SaaS: upload a photo and see yourself with different hairstyles. Users sign in with Google and spend credits on each try-on. Payment webhooks top up those credits and never double-credit, rate limiting keeps usage fair, and images are stored on S3. It runs on Docker with a CI/CD pipeline in GitHub Actions that checks every pull request and deploys to my VPS over SSH.

A practice ground for backend engineers. It has 12 real-world outage scenarios, like slow feeds, backed-up queues and double billing, where you work out what broke and how to fix it.