Google App Engine

With Google App Engine, you can upload your web application and not be stressed with maintaining the servers, everything running on Google's infrastructure. Some of the main features as written in the docs:

• dynamic web serving, with full support for common web technologies
• persistent storage with queries, sorting and transactions
• automatic scaling and load balancing
• APIs for authenticating users and sending email using Google Accounts
• a fully featured local development environment that simulates Google App Engine on your computer

You can download the Google App Engine SDK which includes a web server application that emulates all of the services of the App Engine on your own computer. In addition, there is a YouTube video on a demo describing how to develop and deploy an application on Google App Engine.

At this moment, Google App Engine is in preview release, so space is limited.

**UPDATE**
Google App Engine only supports at this moment web applications written in Python. Other languages will be supported in the future.