"Evolution Data Server manages access to the calendar, tasks and addressbook information available for Evolution and other applications. It is a CORBA component which, when activated, allows concurrent access by several client applications to the same data, adding to that notifications of changes, which are signalled to all clients. Its extensible architecture, allows the addition of plugins to manage different kinds of calendar/tasks/addressbook sources, by just writing a shared library, which will be loaded by evolution-data-server on startup."

On my debian testing installation

  $ apt-rdepends -r evolution-data-server
  Reading package lists... Done
  Building dependency tree       
  Reading state information... Done
  evolution-data-server
    Reverse Depends: contacts (0.9-2+b1)
    Reverse Depends: dates (0.4.8-3)
    Reverse Depends: ekiga (3.2.7-5)
    Reverse Depends: evolution (>= 3.2.2-1+b1)
    Reverse Depends: evolution-data-server-dbg (= 3.2.2-3)
    Reverse Depends: evolution-rss (>= 0.2.90~20111111-3)
    Reverse Depends: gbirthday (0.6.5-1)
    Reverse Depends: gnome-core (>= 1:3.0+9)
    Reverse Depends: gnome-phone-manager (0.68-3)
    Reverse Depends: libfolks-eds25 (>= 0.6.9-1)
    Reverse Depends: libjana-ecal0 (0.0.0+git20091215.9ec1da8a-2+b3)
    Reverse Depends: tasks (0.20-1+b1)