Push service is an online user re-engagement service wherein your website visitors and users receive worthy updates regardless of whether they are present on the browser or not. There are numerous push notification companies presently, most of which provide paid notification services. Some companies provide free push notifications till a certain subscriber count. 

The free web push notification service is provided by Truepush, the world’s most preferred web push service used by 25,000+ brands on a global scale.  

You can send your first push alert by signing up free on https://app.truepush.com/home/register