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.
Cronitor - Monitor cron jobs, micro-services, daemons and almost anything else, no setup required. Easier cron troubleshooting and no more silent failures.
SharpDash - Get an admin dashboard for your product in 5 minutes!
UptimeRobot - Free Website Uptime Monitoring
Robodash - Cron and uptime monitoring dashboard
Cronly - Keep track of your cron jobs and SSL certificates. Don't let them fail unnoticed.