Turba is the Horde contact management application.  It makes heavy
use of the Horde framework to provide integration with other
applications such as the IMP webmail system.

Right now, Turba is a fairly complete basic contact management
application. SQL and LDAP backends are available and fairly well
tested. You can define the fields in your address books in a very
flexible way, just by changing the config files.  And there are
Horde API functions to add and search for contacts.