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.
dradis - Dradis is the open-source reporting and collaboration tool for IT security professionals.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Lampyre - Lampyre - an efficient data analysis and OSINT multi-tool for everyone.
Better Uptime - We call you when your website goes down
SpiderFoot - Open source intelligence (OSINT) automation tool.