I'm using Firebase these days, and I found it very easy to make native apps without coding server side. Firebase gives functions of authentication, analytics, push notifications, database, file storage, etc to developers. Besides, interestingly, the structure of Firestore/Realtime Database is not supposed to be ordinary, it's quite characteristic. Database schema should represent view itself, so normalization is not always good in Firebase. That's so oriented to native app developer.
I made a sample app using Firebase(Firestore, Cloud Messaging, Authentication) like following movie. When a user pushes
Add Button , a new document will be saved in Firestore, and then this update triggers sending push notifications to this user.
Source code is in this repository.