Admin Labs provides powerful monitoring and communication services for businesses.
Healthchecks.io - Monitor your cron jobs and scheduled tasks, get notified when they fail.
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.
Pingbreak - Pingbreak is an original and free monitoring service.
StatusPage.io - StatusPage.io is the best way for web infrastructure, developer API, and SaaS companies to get set up with their very own status page in minutes. Integrate public metrics and allow your customers to subscribe to be updated automatically.
DownDetector - A simple service to tell you whether a website is down.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring