Google Firebase is free to try
Google Firebase is ready for serious, professional backend stack of online software service
It is hard to lean infrastructure and security of online software service, But Google Firebase strongly support those issues.
Google Firebase is "Serverless architecture", So you don't have to maintain server system.
You can focus to implement the idea of your software
Google Firebase supports multiple major software platforms
So, For example, You can start at simple prototyping as Web app, Next you can try to create Android or iOS app
Google Firebase supports multiple major OS for development
List of Firebase feature