asterCRM is a call center software for asterisk based VoIP system, also it has some CRM functions. It provide useful features such as pop-up, predictive dialer, click to call, extension status .... astercrm could work with all asterisk based system.
FreePBX is the most widely deployed Asterisk based PBX application with over 3 million direct and indirect downloads. It transforms your LAMPA stack into a powerful PBX. See http://www.freepbx.org for Forums, Docs, Bug Tracker, Project Site and more.