With Google App Engine, developers can write web applications based on the same building blocks that Google uses, like GFS and Bigtable. Google App Engine packages those building blocks and provides access to scalable infrastructure that we hope will make it easier for developers to scale their applications automatically as they grow. Google App Engine is free to use during the preview release, but the amount of computing resources any app can use is limited. In the future, developers will be able to purchase additional computing resources as needed, but Google App Engine will always be free to get started.
This preview of Google App Engine is available for the first 10,000 developers who sign up.
More details on the Google App Engine Blog.