WebGazer is an uptime monitoring platform that checks if your website is up as it should be and notifies you if anything goes wrong
Clerk - Clerk.io, the artificial intelligence for e-commerce that knows your customers interests.
UptimeRobot - Free Website Uptime Monitoring
Twilio for Slack - Enable SMS conversations with Slack+Twilio
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.
Spike.sh - Spike is an incident management platform that alerts via slack, phone and email and automatic escalations to help teams fix infrastructure problems.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring