Hyperping - Cheap uptime and performance monitoring with detailed reporting and flexible alerting
UptimeRobot - Free Website Uptime Monitoring
UptimeRobot App - Web, SSL, ports & Cron-jobs monitoring
Curler - Dead Simple Free Uptime Monitoring
Cronitor - Monitor cron jobs, micro-services, daemons and almost anything else, no setup required. Easier cron troubleshooting and no more silent failures.
Downtime Monkey - Downtime Monkey: website downtime alerts & uptime monitoring worldwide.