Hi… yeah, it’s true they use their own notification service called MQTT with topic-based notification. You can roll up you own server. If you don’t mind forking out some money, you can use hivemq. It’s easy to setup and reliable with good support. But, if you want to go for open source, you may try a bunch out there. I have tried working with emqtt (erlang mqtt) and it was great. Easy installation, configuration, and provide clustering for scaling purpose.
The downside? Please create an ionic plugin for us I would suggest paho mqtt for java and cocoa mqqt for ios running on swift
Another downside? Although it may be tempting to roll up your own notification server, be remind that the cost is not something to be taken for granted. If you’re still working on your project, try to work around the issue and understand what push really is. Perhaps you can modify your business requirement to not rely on something like push for crucial stuff. Push is not actually made for that. The sooner your realize this, the better. Good luck!!