eds-sync is one of the many components that you don't see on the Nokia N800, but is essential to the integrated chat/voip interface. It's role is basically to do full two-way synchronisation between any number of remote rosters (generally Jabber/XMPP rosters on the N800) and the Evolution Data Server addressbook. It also downloads avatars, so that they are available on disk for display in applications.

NP: Live at the Jazz Café, Fink