Bitcalm - Backup service for your servers
Hyperping - Cheap uptime and performance monitoring with detailed reporting and flexible alerting
Dead Man's Snitch - Monitor Cron Jobs and Windows Scheduled Tasks with ease.
Cronitor - Monitor cron jobs, micro-services, daemons and almost anything else, no setup required. Easier cron troubleshooting and no more silent failures.
Healthchecks.io - Monitor your cron jobs and scheduled tasks, get notified when they fail.
UptimeRobot App - Web, SSL, ports & Cron-jobs monitoring