This year I built Calendo, a scheduling app like Calendly, by myself. Last week I open-sourced it under AGPL. Here is how it's built and what I learned.

The setup

Everything runs on Cloudflare Workers. The database is D1, which is SQLite. The frontend is plain HTML, CSS and JavaScript. There is no React, no bundler and no build step. You edit a file and deploy.

I chose this for three reasons:

Cost. The Workers free tier covers a lot of traffic. Serving a user costs me a fraction of a cent a month, so core scheduling can be free.

Nothing to break. No framework upgrades. Code I write today will still run in two years.

Easy to read. Any developer (or AI coding tool) can open a file and understand it.

The trade-off is more manual DOM code. For a solo project it has been worth it.

The AI agent

The dashboard has an AI agent.…