Notif.me SDK - A Node.js lib to send all your transactional notifications
Pusher Beams - Send push notifications programmatically at scale
Ethereum Push Notification Service - Protocol for incentivized, blockchain based notifications.
Instapush - Instant notifications for transactions that matter.
Pragma - The home base for Ethereum developers.
CryptoNotify - Receive transaction notifications of any BTC or ETH address