Notif.me SDK - A Node.js lib to send all your transactional notifications
Pushover - Real-time notifications on your Android, iPhone, iPad, and Desktop
Pusher Beams - Send push notifications programmatically at scale
Instapush - Instant notifications for transactions that matter.
CryptoNotify - Receive transaction notifications of any BTC or ETH address
Ethercast - Get notifications for events on the Ethereum blockchain