WHMCS is an all-in-one client management, billing & support solution for online businesses. WHMCS handles everything from signup to termination, with automated billing, provisioning & management.
This integration module was written by WHMCS themselves and is currently the only official integration from WHMCS to a web-based accounting application.
The module copys across invoices and customer information from WHMCS into KashFlow. It then continues to update as new invoices and customers appear in WHMCS.
For more information, visit: http://wiki.whmcs.com/KashFlow_Accounting