Notif.me SDK - A Node.js lib to send all your transactional notifications
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Ethereum Push Notification Service - Protocol for incentivized, blockchain based notifications.
Truepush - Unleash limitless possibilities with Truepush and save up to $600 monthly. Free up to 10K Subscribers on all features.
Blockbutler - Real-time transaction notifications for the blockchain
PushOwl - Re-engage website visitors with push notifications