I think every smartphone user knows what is push notification. It's very useful tool for user-engagement and productivity.
But use custom push notifications you need
1) mobile device client (app)
2) mobile backend
Jeapie - is a product that solves this problem.
It's a ready-to-use mobile app (Android, iOS soon) and a web-service that translates HTTP request to PUSH notification.
Raw example (shell):
And we published a class for implementing in custom projects.
Example of usage: