UptimeRobot - Free Website Uptime Monitoring
HackerOne - HackerOne provides a platform designed to streamline vulnerability coordination and bug bounty program by enlisting hackers.
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.
Trustwave Services - Trustwave is a leading cybersecurity and managed security services provider that helps businesses fight cybercrime, protect data and reduce security risk.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Acunetix - Audit your website security and web applications for SQL injection, Cross site scripting and other...