NetBox - NetBox is an open source web application designed to help manage and document computer networks. NetBox was developed specifically to address the needs of network and infrastructure engineers.
Zabbix - Track, record, alert and visualize performance and availability of IT resources
Snipe-IT - Managing assets with a Google doc or a shared Excel spreadsheet is more common than you think.
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.
Prometheus - An open-source systems monitoring and alerting toolkit.
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.