Notif.me SDK - A Node.js lib to send all your transactional notifications
CryptoNotify - Receive transaction notifications of any BTC or ETH address
Pusher Beams - Send push notifications programmatically at scale
The Simple Postcard - Text a photo to mail it as a postcard
Ethercast - Get notifications for events on the Ethereum blockchain
ZeroPush - Simple Push Notifications for Developers