Address Book Continued provides a multi-user AJAX address book Web application.
It also makes use of AJAX, which means that page reloads only happen on login/logout; the rest of the operations is handled asynchronously in the background. It's well usable, even over slow connections.
You can even install ABC on your desktop PC and configure it so that it doesn't require login for connections coming from the local computer.
1. Execute the content of create-databases.sql on your MySQL server. Create a
user that can do SELECT, INSERT, UPDATE and DELETE on the new database.
2. Modify configuration.php to contain valid MySQL access data.
3. Copy the contents of the directory web onto your web server.