RackTables - Racktables is a nifty and robust solution for datacenter and server room asset management.
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.
Racksmith - RackSmith is designed to provide an easy to use web interface to manage equipment and connections...
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
Opendcim - a free, web based Data Center Infrastructure Management application.