Is It Down Right Now? - Network & Admin
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.
UPDOWNtoday - UPDOWNTODAY allows you to check whether the website is down or not.
Hosted Status Page - Incident Management with Automated Downtime Detection
IsThisSiteDown.org - Free tool to check whether a site is down just for you, or for everyone.
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.