OneSignal - Customer engagement platform used by over 1 million developers and marketers; the fastest and most reliable way to send mobile and web push notifications, in-app messages, emails, and SMS.
Pusher Beams - Send push notifications programmatically at scale
Truepush - Unleash limitless possibilities with Truepush and save up to $600 monthly. Free up to 10K Subscribers on all features.
Pingy - Check your site status from your menubar
PushCrew - Push Notifications for Websites
Snowball Smart Notifications - Get the notifications you want and none of the rest