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.
PushBots - Light SDK for mobile push notifications
PushCrew - Push Notifications for Websites
iZooto - Engage your mobile and desktop web users with intelligent web push notifications.
Amazon SNS - Fully managed pub/sub messaging for microservices, distributed systems, and serverless applications
Batch - Batch is an intelligent push notifications platform for mobile apps.