A fork of SugarCRM, vTiger is a powerful CRM with a host of features. There's only one edition, which is free and open source. In addition to the standard CRM capabilities, it includes what would be considered premium features in other CRM apps: sales orders, purchase orders, invoices, asset tracking, SMS notification, PBX manager, customer portal, mobile access, and workflows, to name a few. The community is large and active, and there's a lot of good documentation, plenty of third-party add-ons, and a new project called Tigress for making modifications without requiring code change. An inexpensive hosted version and third-party integration with Front Accounting are also available.
-- Fred Blauer