WHMCS is an excellent web hosting billing software. When I googled about WHMCS Free License, I found that the only way to obtain genuine free license is to purchase specified products at WHMCS's cooperative companies like HostGator, Surpass, HostDime and return to whmcs.com to sign up for a Web Host license.
However, after several days' research, I figured out a way to obtain free license without hosting at them, and you can pass the domain verification at http://www.whmcs.com/members/verifydomain.php. you can go to my blog to read more: [link removed]
If you have any question about this just let me know. For test purpose only. :)