What is Google GCM?
Google Cloud Messaging (GCM) is a service that enables developers to send data from servers to both Android applications or Chrome apps and extensions.
What is Apple APNS?
The Apple Push Notification Service (APNs) is a service created by Apple Inc. that was launched together with iOS 3.0 on June 17, 2009. It forwards notifications of third party applications to the Apple devices; such notifications may include badges, sounds or custom text alerts.
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