From CloudWiki
Google AppEngine
App Engine is the Google approach to cloud computing: empower developers to build, maintain and scale Web applications without hassle. Different from Amazon-style cloud computing the App Engine is a fully fledged Web application deployment platform with persistent storage, automatic load balancing and scaling, as well as a hand full of special-purpose APIs that let developers integrate useful features, such as E-Mail communication and image manipulation.
Datastore
To start with: the App Engine datastore is not a relational database. Instead, the datastore can be thought of as a giant, scalable spreadsheet with one entity in each row and the entities' typed properties as columns. With an SQL-like query language, named GQL, you can perform queries over the entities.
Special APIs
Google offers a couple of special-purpose APIs, that help developers to integrate features, such as E-Mail infrastructure and image manipulation.
