open source customer relationship management system CRM

SourceForge.net: Project Info - SugarCRM
customer relationship management is an area that enormous amounts of money have been spent on. most of that money is marketing. I suggest you look at an open source package that allows you to test implement and even run production environments on this platform. if you desire a level of support there is a commercial fork of the package which should satisfy anyone looking for an invoiceable item.

SugarCRM v3.5 beta released on August 1st. A fully featured customer releationship management (CRM) system. Manage leads, opportunities, contacts and more inside of a state-of-the-art user interface. Built on PHP and MySQL. See home page for demo.