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.
RackTables - Racktables is a nifty and robust solution for datacenter and server room asset management.
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
Ralph - Ralph is full-featured Asset Management, DCIM and CMDB system for data center and back office.
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.