Hyperping - Cheap uptime and performance monitoring with detailed reporting and flexible alerting
EasyCron - Get frustrated with Cron on your server? Hosting limits your Cron use?
UptimeRobot App - Web, SSL, ports & Cron-jobs monitoring
crontab guru - The quick and simple editor for cron schedule expressions by Cronitor
Cronitor - Monitor cron jobs, micro-services, daemons and almost anything else, no setup required. Easier cron troubleshooting and no more silent failures.
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.