Give me some open source code that I can run on my own server to manage the notifications for me and for my friends, and allow me to tell the client app on my p

Give me some open source code that I can run on my own server to manage the notifications for me and for my friends, and allow me to tell the client app on my phone to use it. That's way better than forcing me to rely on a specific Google server and protocol, which further requires proprietary software on the client.