Pushover

Pushover is a simple notification tool, offering real-time notifications to users on their Android, iPhone, iPad, and Desktop, as well as Android Wear and Apple Watch. In addition to its Android and iPhone/iPad mobile client apps, Pushover can deliver notifications to a desktop with a web-based application. By having the web client open in Google Chrome, Mozilla Firefox, or Apple Safari web browser1, the user can receive popup notifications on a desktop just like mobile devices. For users of macOS 10.9 (Mavericks) or higher, push notifications can be delivered to a desktop, lock screen, and Notification Center without needing any web browser to be open (requires initial registration through the Safari web browser).