Blockbutler - Real-time transaction notifications for the blockchain
Pushover - Real-time notifications on your Android, iPhone, iPad, and Desktop
CryptoNotify - Receive transaction notifications of any BTC or ETH address
Pusher Beams - Send push notifications programmatically at scale
Notif.me SDK - A Node.js lib to send all your transactional notifications
The Simple Postcard - Text a photo to mail it as a postcard