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.
Firebase - Firebase is a cloud service designed to power real-time, collaborative applications for mobile and web.
PushBots - Light SDK for mobile push notifications
iZooto - Engage your mobile and desktop web users with intelligent web push notifications.
Parse - Build applications faster with object and file storage, user authentication, push notifications, dashboard and more out of the box.
PushCrew - Push Notifications for Websites