ntfy is a simple HTTP-based pub-sub notification service. It allows you to send notifications to your phone or desktop via scripts from any computer, and/or using a REST API.
Thanks, i did not know about MQTT! (https://mqtt.org/ for others like me) Looks great, at first glimpse harder to use, but i will give it a honest shot.
are there any notifications that don't come from separate apps? System notifs perhaps, but one could argue they come from the "system apps". I figure this system is specifically designed for personalised notifications from things one administer independently. Such as backups, home-server monitoring, sovereign home appliances etc... I'm not codelitrary enough to figure out whether this can be built in to a 3rd party app, but i imagine it to be possible but would require a server somewhere eitherway. Kind of like NextcloudServices offers (Simply fetch Nextcloud notifications on devices without Google Play services)
https://f-droid.org/packages/com.polar.nextcloudservices/
Otherwise the closest thing would be leveraging the browser notification API. Still an app, but at least one that most users have installed (see https://fed.dyne.org/comment/53589)
ah yes, ametyst also (nostr client, that's how i found out about it) I guess what i wondered was, to what extend it would be possible to integrate the system inside an app, without having the user install an extra app...