ntfy

ntfy is a server that accepts messages over HTTP and delivers them as push notifications to phones, desktops and browsers. A script or application publishes to a topic with a PUT or POST request, and the apps and web app subscribed to that topic show the message. The server ships as a binary, a Docker image or a package, and its install guide describes running it as a permanent service. It can keep its data in SQLite or PostgreSQL.

The project also runs a public server, ntfy.sh, and the software can be self-hosted.

Worth knowing

Without sign-up, a topic on the public server works like a password: the homepage says so and advises a name that is hard to guess. The public server also offers paid plans next to a free tier.