Existing users, 
HDD/Users/[You]/Library/Application Support/Address Book
Place in same location on any other Mac, restart Address Book, and BAM, you're sync'ed for free.
Address Book Server
Share contacts & calendar events between Mac and the Web.
Version: 30 October
For free...
Feedback Type: Commentary
Contributed by: W-Creative Monday, March 02 2009 @ 02:15 AM PST
Product Platform: MacOSX
Used Product For: Have Not Tried
Comments
For free... - ceisler
That doesn't sync multiple address books, it only installs the same set of addresses on all computers.Thursday, May 28 2009 @ 09:39 AM PDT
For free... - lostinspace2011--2008
Address Book Server lets you share contacts between network'd macs, while this suggestion only seems to work with accounts on the same mac.Wednesday, August 26 2009 @ 02:54 PM PDT
For free... - julia2
Well, no - overwriting a file with another file is not the same as synchronizing two files. Changes made in the file that gets overwritten are lost. Or am I missing something in your suggestion?Reply to This
Monday, March 02 2009 @ 12:10 PM PST