Hyperping - Cheap uptime and performance monitoring with detailed reporting and flexible alerting
Healthchecks.io - Monitor your cron jobs and scheduled tasks, get notified when they fail.
UptimeRobot App - Web, SSL, ports & Cron-jobs monitoring
Cronitor - Monitor cron jobs, micro-services, daemons and almost anything else, no setup required. Easier cron troubleshooting and no more silent failures.
Cronly - Keep track of your cron jobs and SSL certificates. Don't let them fail unnoticed.
Cronhub - Cronhub helps you to easily monitor all your cron jobs in a beautiful dashboard. It alerts you when your cron job doesn't run on time or it fails.