As I said two posts back we use the Community Edition of SugarCRM as our Customer Relationship Management system. SugarCRM is very good and it has a good community behind it. There have been a lot of modules written that extend SugarCRM in various ways, many of which interact with other online systems. I have added a couple to our install of SugarCRM recently. They are connectors that allow interaction with Dimdim and Google Calendars.
One of the more useful Open Source tools we use is SugarCRM. SugarCRM is a Customer Relationship Management system (CRM). A CRM is used to track and organise contacts with current and potential customers or clients.