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.
Azure Network Watcher - Azure Network Watcher provides multiple features to help you visualize key parameters, track, troubleshoot, and activate or deactivate logs for resources in an Azure virtual network.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Obkio - Simple Network Monitoring and Network Troubleshooting software to empower users to identify and troubleshoot network & application slowdown from the end-user perspective.
Better Uptime - We call you when your website goes down
SevOne - SevOne provides network managers with monitoring, troubleshooting, and performance reporting capabilities.