Now Push Notify - iOS does not support browser notifications today, but Now Push Notify makes this possible.
Pusher Beams - Send push notifications programmatically at scale
Push Notification Preview - A simple tool for previewing push notification copy
PushNinja - by 500apps
Ultimate Push Notifications by Ecomfit - Retarget customers and protect abandoned cart to boost sale
Analyzify - Google tag manager and analytics app for your Shopify store