Anturis - Anturis offers hosted server monitoring software (SaaS) for both Windows and Linux.
Zabbix - Track, record, alert and visualize performance and availability of IT resources
Zohno Z-Term - The Easy-to-Use Active Directory User Termination Tool
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.
NIXStats - SaaS monitoring tool for window/linux servers and websites. Think up-time robot but with more features.
Prometheus - An open-source systems monitoring and alerting toolkit.