The Evolution Data Server package provides a unified backend for programs that work with
contacts, tasks, and calendar information. It was originally developed for Evolution
(hence the name), but is now used by other packages as well. 

The Evolution Data Server provides a single database for common, desktop-wide information,
such as a user's address book or calendar events.

By using the evolution-data-server, other GNOME applications are integrating with Evolution.

  * gnome-panel calendar applet lists your appointments and tasks.
  * Synchronize your Pidgin buddies with your Evolution contacts.
  * View Planner files as Evolution task lists.