WP Umbrella - The easiest way to manage multiple WordPress websites effortlessly.
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.
Datafold - Quality assurance & monitoring for analytical data
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Masthead Data - Masthead Data helps data teams to identify and fix data errors before they become a problem for data consumers. It catches anomalies in the data warehouse in real time.
Better Uptime - We call you when your website goes down