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.
Letterun - Get your favorite newsletters without email or subscriptions
PushBots - Light SDK for mobile push notifications
Snack - Read all your favorite email subscriptions in one app
iZooto - Engage your mobile and desktop web users with intelligent web push notifications.
Supscrib - The new way of subscribing to newsletters