Address-o-Sync

Address-o-Sync is a Rendezvous-enabled application to sync Address Book entries across several Macs. I'm not sure how secure it is (I don't think it encrypts data on the LAN), but it does a number of neat things:

• Share only certain groups created in the Address Book
• Only syncs new or modified entries (and warns you of changes)
• Groups made accessible are still password protected