Lansweeper - Lansweeper discovers Windows, Linux and Mac machines in your network.
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.
Spiceworks Help Desk - Help desk software features that work for IT
Snipe-IT - Managing assets with a Google doc or a shared Excel spreadsheet is more common than you think.
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.
Zabbix - Track, record, alert and visualize performance and availability of IT resources