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.
Total Network Inventory - Total Network Inventory is a piece of software designed to help with managing software inventory and auditing PC systems.
Snipe-IT - Managing assets with a Google doc or a shared Excel spreadsheet is more common than you think.
Lansweeper - Lansweeper discovers Windows, Linux and Mac machines in your network.
Zabbix - Track, record, alert and visualize performance and availability of IT resources
Spiceworks Help Desk - Help desk software features that work for IT