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