Healthchecks.io - Monitor your cron jobs and scheduled tasks, get notified when they fail.
NIXStats - SaaS monitoring tool for window/linux servers and websites. Think up-time robot but with more features.
Cronitor - Monitor cron jobs, micro-services, daemons and almost anything else, no setup required. Easier cron troubleshooting and no more silent failures.
Server Monitoring - A server monitor is a tool that monitors your server and website on close intervals and reports to you if it's inaccessible.
Cronotary - Painless periodical tasks monitoring. Cronotary makes sure your background jobs are up and running.
Nodeping - NodePing Server Monitoring and Web Site Monitoring. Simple but powerful Internet service monitoring.