A number of tools have been developed to facilitate the sharing of contact information for OS X users. The tools are geared for small to medium sized environments which require individuals to contribute to, and access a centrally shared address book. Several iterations of the tools address different aspects and options. The projects rely heavily on input from the user community and support.

No need to wait for Snow Leopard Server. With Address Book Server you can already sync your contacts between Macs today. We support 10.4 (Tiger), 10.5 (Leopard) on both Intel and PowerPC. Unlike 10.6 (Snow Leopard) which will require Intel hardware, we already have a solution ready today. Address Book Server does not require any subscription or charges. Upgrades have so far been free, which is a trend we will try to continue going forward. Take control of your contacts today on your existing investment.
Address Book and Calendar Server

Address Book Server allows you to share your contacts and calendar events with others connected to your network or over the internet. Each participants synchronizes their contacts with the server hosted own your own system. Address Book and Calendar Server supports the full Address Book and iCal Schema. The server also provides a friendly web interface which you can use to access your contact details when you not on your Mac. There is even an iPhone client which accesses the contact details on the server directly for when you on the road.