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.
Lansweeper - Lansweeper discovers Windows, Linux and Mac machines in your network.
Snipe-IT - Managing assets with a Google doc or a shared Excel spreadsheet is more common than you think.
Zabbix - Track, record, alert and visualize performance and availability of IT resources
FusionInventory - Fork of the OCS Inventory project that enables users to inventory their IT assets.
RackTables - Racktables is a nifty and robust solution for datacenter and server room asset management.