PhpCoin

PhpCoin, once known to be exclusively used by hosting resellers, is a free web-based control panel designed to handle clients, orders, invoices, notes and helpdesk.

PhpCoin claims to be used by over thirty-five thousand people worldwide, and is a good way to run a control panel without paying any costs to set up, maintain, or install.

From their website:

Price: phpCOIN version 1.x is 100% free of cost to use ~ although donations to help cover the time and expenses of running this site are appreciated. When it is available, phpCOIN v2 will be free to use for up to ten active clients, but more then ten active clients will require a fee.

Website: www.phpcoin.com