Pushbullet is an Android app that allows users to send notifications between devices and receive them from the internet. You can also subscribe to channels to receive mobile notifications when new content is posted (much like an RSS or atom feed).
Adding Pushbullet to N8n would allow Android users to easily integrate mobile notifications to their workflow.
The API documentation is available and looks pretty good. I haven’t looked at it in details yet
Native notifications would be a topic for another suggestion. It’s possible but complicated when dealing with something that can be self hosted and not fully under the control of one developer.