Windows Azure Mobile Services (currently preview release) allow you to connect your Windows 8 apps to a cloud backend hosted in Windows Azure and easily store structured data, authenticate users, and send push notifications.
To start using Mobile Services, you will need to sign up for the Windows Azure free trial, if you have not done so already. If you already have a Windows Azure account, you will need to request to enroll in this preview feature. During preview, Mobile Services are free for your first ten Windows 8 applications running on shared instances.
Creating and using a Mobile Service is Easy. See detail at Get started with Mobile Services