Anyone Familiar with Open Source CRM Systems?

I'd like to set up a Customer Relationship Management (CRM) system to manage the department's contact list, help with event planning, and so on. Key requirements are ease of use (most people will only touch it occasionally, so the interface has to be intuitive on a once-a-month basis), and ease of installation and management. Systems that look plausible include: Anyone have any experience or recommendations to share?