WHMCS - WHMCS is an all-in-one client management, billing & support system for online businesses.
HostBill - HostBill is a powerful and flexible, all-in-one automation, billing, client management and support platform for online businesses.
BoxBilling - Complete client management, billing & support software.
BILLmanager - BILLmanager is an all-in-one web hosting billing software. It provides billing automation, service provisioning, client portal & back office and support center.
NUKERN - Set your web hosting services on autopilot
Blesta - Blesta is professional client management, billing, and support software.