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.
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PushCrew - Push Notifications for Websites
OneSignal Push Notifications for Shopify - Abandoned cart, automated campaigns, robust analytics.
Notix.co - NOTIX is an audience re-engagement service based on web and in-app push notifications that work for both desktop and mobile devices.
Pusher Beams - Send push notifications programmatically at scale