Main Page – Fedora Directory Server
“Welcome to the Fedora Directory Server. The Fedora Directory Server is a robust, scalable open-source server designed to manage large directories of users and resources. It is based on an open-systems server protocol called the Lightweight Directory Access Protocol (LDAP).“
This could be used in place of commercial products like Microsoft Active Directory and Novell eDirectory. It is enterprise grade stuff, so it isn’t for the ‘I need an addressbook’ OpenLDAP crowd.