Firebase

Data & backend

Firebase

Firebase is a Backend-as-a-Service (BaaS) app development platform
that provides hosted backend services such as a realtime database,
cloud storage, authentication, crash reporting, machine learning,
remote configuration, and hosting for your static files.

Firebase supports Flutter. For more information, see:

The Firebase plugins page

Getting started with Firebase and Flutter

Get to know Firebase for Flutter video workshop
based on the codelab

Get to know Firebase for Flutter codelab

Use Firebase to host your Flutter app on the web

Also, the Flutter community has created docs and
videos that you might find useful. Here are a few:

Building chat app with Flutter and Firebase

Using Firestore as a backend to your Flutter app (video)

Live Coding Firebase Authentication with Flutter (video)