Open Source Contact Manager (something like ACT?)

[hewitt_tech]

Has anyone any experience with an open source contact manager application 
something like ACT! ? I searched Sourceforge and got a few hits but I 
haven't any idea as to how good any of these projects migh be. One that 
sound's like it might fit the bill is CalypsoRCP. The application would 
probably service a half dozen or so users hosted on Windows systems.

-Alex