Notif.me SDK - A Node.js lib to send all your transactional notifications
Pragma - The home base for Ethereum developers.
Pusher Beams - Send push notifications programmatically at scale
Pusher - Pusher is a hosted API for quickly, easily and securely adding scalable realtime functionality via WebSockets to web and mobile apps.
Instapush - Instant notifications for transactions that matter.
Clank - Explore the biggest crypto transactions across blockchains