UptimeRobot - Free Website Uptime Monitoring
Ahrefs Backlink Checker - With the world's biggest index of live backlinks (over 15 trillion), Ahrefs Backlink Checker will show you the most complete backlink profile for any website.
Hyperping - Cheap uptime and performance monitoring with detailed reporting and flexible alerting
Backlinks by Neil Patel - A backlinks research tool for competitive intelligence
UptimeRobot App - Web, SSL, ports & Cron-jobs monitoring
Toxic Backlink Checker - Find out what's lurking in your backlink profile.