RackTables - Racktables is a nifty and robust solution for datacenter and server room asset management.
WHMCS - WHMCS is an all-in-one client management, billing & support system for online businesses.
DCImanager - DCImanager is a platform for managing physical equipment. Connect any physical equipment to a single platform. Use the platform to manage your servers, switches, PDU as well as physical and virtual networks.
HostBill - HostBill is a powerful and flexible, all-in-one automation, billing, client management and support platform for online businesses.
Opendcim - a free, web based Data Center Infrastructure Management application.
Blesta - Blesta is professional client management, billing, and support software.