Cloud Firestore in Datastore mode is a NoSQL document database built for automatic scaling, high performance, and ease of application development.
Cloud Firestore is the newest version of Cloud Datastore and introduces several improvements over Cloud Datastore. Existing Cloud Datastore users can access these improvements by creating a new Cloud Firestore in Datastore mode database instance. In the future, all existing Cloud Datastore databases will be automatically upgraded to Cloud Firestore in Datastore mode.
While the Datastore mode interface has many of the same features as traditional databases, as a NoSQL database it differs from them in the way it describes relationships between data objects.
Not sure what storage option is right for you? Check out the Choosing a Storage Option guide.