Google's newest offering Google App Engine lets you use Google's infrastructure for hosting your applications online, the service currently released as a PREVIEW for first 10,000 developers allows participants to use Google's highly scalable fully-integrated application environment with upto 500MB of persistent storage and enough bandwidth and CPU for 5 million monthly page views for free.

The Google App Engine platform consists of Python application servers and BigTable database servers, only free accounts are available for now but you will be able to purchase additional computing resources in near future, only Python is supported now but much more is expected in future.