ntfy

ntfy is a tiny publish and subscribe notification service where you send a message with a simple HTTP request to a topic URL and it is pushed to subscribed phones, desktops, and browsers. Topics can be protected with tokens, and clients support priorities, actions, scheduled delivery, and attachments, so it covers considerably more than plain text alerts.

People use it in place of SMS for server pings, build and deploy notifications, home automation events, and quick personal reminders.

Running it yourself on your own hardware keeps the content of your alerts private, avoids the per-message fees of a hosted push provider, and makes the small SQLite state easy to snapshot and restore.