Notanotifier is an amazing app for those who love watching live matches on DotaTV

Features (fan DotA2):
- List Pro Players in the world.
- Click to follow Pro Players you love
- Notify when followed players start new live matches

It is an open-source app, you can learn:
- working with Firebase, Firebase Cloud Messaging (FCM) for push notification
- Working with RESTful API
- The server-side code is also open-source, you can build your own server app.

It is a full-stack open source app, check it out.