Pusher Beams - Send push notifications programmatically at scale
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.
Mentioned By - Learn when your site is mentioned by other sites for free
PushCrew - Push Notifications for Websites
Now Push Notify - iOS does not support browser notifications today, but Now Push Notify makes this possible.
Notix.co - NOTIX is an audience re-engagement service based on web and in-app push notifications that work for both desktop and mobile devices.