OpenPush - A Free, Decentralized Push Messaging Framework
A Google Cloud Messaging (GCM) /Firebase Cloud Messaging (FCM) REPLACEMENT
OpenPush is a self-hosted, free alternative push messaging implementation which can either run alongside or as a replacement to FCM.
OpenPush was presented at FOSDEM. The talk gives a general architecture overview as well as walks through the design and implementation challenges of a push messaging service.
OpenPush Article more links in article
OpenPush Project Website