UnifiedPush is a set of specifications and tools that lets the user choose how push notifications* are delivered. All in a free and open source way.
- I JUST WANT TO KNOW WHAT TO INSTALL: ntfy (Android)
- The same but I must use Google for some reason (hard battery optimization): UP-FCM Distrib (Android)
- I have a Nextcloud server: NextPush (Android)
- For other options, see below.