Описание тега azure-notificationhub
A Microsoft Azure service which enables very-high-scale push notifications to Windows, Windows Phone, iOS, Android, and future platforms, using either native payloads or templates, and tags to target broadcasts widely or narrowly.
According to MSDN: http://msdn.microsoft.com/en-us/library/jj891130.aspx:
Notification Hubs are an Azure service which "enable you to access an easy-to-use, multiplatform, scaled-out push infrastructure, which simplifies the implementation of push notifications for both consumer and enterprise apps on mobile platforms."
Azure Notification Hubs abstracts the complexities of working with Windows Notification Services, Windows Mobile Notification Services, Apple Push Notification Services, and Google Cloud Messaging, so that a single method call can conceivably target any one device, or all of the devices, regardless of the device platform.
Marketing page with feature descriptions: http://azure.microsoft.com/en-us/services/notification-hubs/