Pusher Beams - Send push notifications programmatically at scale
Pingdom - With website monitoring from Pingdom you will be the first to know when your website is down. No installation required. 30-day free trial.
PushOwl - Re-engage website visitors with push notifications
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Pusher - Pusher is a hosted API for quickly, easily and securely adding scalable realtime functionality via WebSockets to web and mobile apps.
Better Uptime - We call you when your website goes down