Firebase Cloud Messaging
Firebase Cloud Messaging (commonly referred to as FCM), formerly known as Google Cloud Messaging (GCM), is a cross-platform cloud solution for messages and notifications for Android, iOS, and web applications, which currently can be used at no cost.
The service is provided by Firebase, a subsidiary of Google. On 21 October 2014, Firebase announced it had been acquired by Google for an undisclosed amount. The official Google Cloud Messaging website points to Firebase Cloud Messaging (FCM) as the new version of GCM.