osTicket - osTicket is a widely-used open source support ticket system.
Zabbix - Track, record, alert and visualize performance and availability of IT resources
Freshdesk - Freshdesk is a cloud-based customer support software that lets you support customers through traditional channels like phone and email, social channels like Facebook and Twitter, and your own branded community
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.
OpenRMA - Computer Repair Shop Software. Mobile Repair shop Software and any king of repair shop. Track computer, mobile, tv, jewelry, bike repairs and any king of repair shop.
Prometheus - An open-source systems monitoring and alerting toolkit.