This Google Developers tutorial explores App Engine's Datastore service, driven by Google Bigtable:
Datastore service in App Engine is the core component of the platform and an essential part of learning App Engine technologies. In this lesson we will cover topics including "What is Datastore?", "Datastore Internals" and "Datastore Basic Operation". We will be looking at basic concepts including the difference between a Relational Database and Datastore, scalability, reliability and performance characteristics of Datastore. We will also dive deeper into the underlying technology, Google Bigtable. As basic operations, we will learn Datastore concepts like Entity, Property and Key as well as Datastore APIs.