Site24x7 - Site24x7 offers both free & paid website monitoring services. Monitor websites remotely and receive instant email/sms alerts if your website becomes unavailable. View uptime & performance graphs of your website monitors.
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.
ScienceLogic - ScienceLogic simplifies data center, cloud, and network monitoring with its all-in-one platform.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
InsightCat - Full-stack monitoring platform for your software and hardware. InsightCat is a cloud-based and AI-powered solution to enhance your system health estate through infrastructure monitoring and alerting capabilities.
Better Uptime - We call you when your website goes down