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.

Status.io - Status.io is a platform for system status pages and status notifications. Companies rely on Status.io to track outages, schedule planned maintenances, broadcast status notifications, and much more; and their customers love the transparency.

Pingbreak - Pingbreak is an original and free monitoring service.

StatusHub - StatusHub is an IT Incident & Disruption Communication tool that helps you keep your customers and team informed during service downtime. StatusHub makes it easy to keep everyone informed through status pages and multiple notification channels.

DownDetector - A simple service to tell you whether a website is down.

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.