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.
PushEngage - Personalized Browser Push Notifications.
PushBots - Light SDK for mobile push notifications
Truepush - Unleash limitless possibilities with Truepush and save up to $600 monthly. Free up to 10K Subscribers on all features.
iZooto - Engage your mobile and desktop web users with intelligent web push notifications.
Gotify - a simple self-hosted server for sending and receiving messages