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.
Warply - A mobile marketing toolbox that powers up monetization, loyalty and engagement.
Pusher Beams - Send push notifications programmatically at scale
Parse - Build applications faster with object and file storage, user authentication, push notifications, dashboard and more out of the box.
Pushy - Pushy is a reliable push notification gateway for time-sensitive, mission-critical apps.