What are the applications aggregating push notifications from services?

Question

Android

The task is to make push notifications to customers' phones. Sends their server to some server via API. I would like to do without the development of an android application (plus I still need to write to the apple ...), but only for the client to install a certain aggregator, add my service, my identifier to it, and that's it. So far, everyone around offers only SDK... but there is no time to develop for android|iOS.
If the application is paid, it would be optimal if the client was free, and if I would pay for sending notifications.
While I'm thinking in the direction of Telegram - register a client for a certain number, and add a list of message recipients to the contact ..

Answer 1

boxcar.io
prowlapp.com
notifymyandroid.com
pushover.net
Another option is to send browser push notifications via Chrome if you only need Android.