Bitcalm - Backup service for your servers
Platypus - Realtime server monitoring and reporting
Dead Man's Snitch - Monitor Cron Jobs and Windows Scheduled Tasks with ease.
Datadog - See metrics from all of your apps, tools & services in one place with Datadog's cloud monitoring as a service solution. Try it for free.
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.
Nagios - Complete monitoring and alerting for servers, switches, applications, and services