KDE Connect - Integrate Android with the KDE Desktop
Pushover - Real-time notifications on your Android, iPhone, iPad, and Desktop
Pushbullet - Pushbullet - Your devices working better together
mconnect - Vala/C implementation of KDE Connect
Gotify - a simple self-hosted server for sending and receiving messages
AirMore - AirMore is a cross-platform toolset that can help you manage any Android device wirelessly.