389 Directory Server suite - server

 Based on the Lightweight Directory Access Protocol (LDAP), the 389
 Directory Server is designed to manage large directories of users and
 resources robustly and scalably.
 .
 Its key features include:
  * four-way multi-master replication;
  * great scalability;
  * extensive documentation;
  * Active Directory user and group synchronization;
  * secure authentication and transport;
  * support for LDAPv3;
  * graphical management console;
  * on-line, zero downtime update of schema, configuration, and
    in-tree Access Control Information.