Looks very nice. Best of luck.

For me, the killer feature for any pushover competitor would be support for actionable notifications which trigger a webhook callback when the button is clicked.

To be honest, I'm not sure that's even possible with iOS's notification framework. I don't know whether the notification payload can define which buttons are displayed, or if they need to be defined ahead of time in the app. But if it could be done I would be all over it.