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.
SashiDo.io - SashiDo is the Parse Alternative for busy people.
PushBots - Light SDK for mobile push notifications
SmartPush - SmartPush is a push notification service provider that helps businesses increase customer engagement using web push notifications.
PushCrew - Push Notifications for Websites
Pushy - Pushy is a reliable push notification gateway for time-sensitive, mission-critical apps.