Zabbix - Track, record, alert and visualize performance and availability of IT resources
Issuetrak - Issue tracking software for help desk and customer service
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.
Deskun - Deskun is a Help Desk system inside Gmail. It enables you to support customers directly from your mailbox, manage projects, and use free features for Gmail.
Prometheus - An open-source systems monitoring and alerting toolkit.
Kapdesk - Kapdesk offers support teams with a helpdesk software to streamline support tasks.