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.
NUKERN - Set your web hosting services on autopilot
Blesta - Blesta is professional client management, billing, and support software.
TheHostingTool - TheHostingTool was launched on the 3rd of December 2008 aiming to provide the next generation in...
InvoicePlane - Free and open source invoicing application to host on your own server.