Services like Google’s Firebase Cloud Messaging (FCM) and Apple’s APNS are the base for push notifications.
These services enable notifications on Safari, and Windows Notification Service for Microsoft Edge. 

source

Taking FCM as an example, it’s a messaging solution that allows websites and mobile applications to send push notifications to subscribers. The subscriber’s data, along with the notification content, is sent to the FCM through App Server. The information is then verified by the FCM and sends notifications to the end user’s devices. The important data, such as total clicks, total views, along with other relevant data, is then sent through devices to the application server.

To send free push notifications to your user, sign-up to Truepush now.