Is there a Linux equivalent of Microsoft's Active Directory?

Microsoft Windows has Active Directory. Is there anything similar in the Linux world?
LDAP or OpenLDAP. Novell's NDS (Novell Directory Services) with SuSe will also become a player. JLDAP, which is in SuSE and Red Hat (the LDAP class libraries for Java) which is LDAPv3. An alternative to Active Directory would be LDAP (Lightweight Directory Access Protocol) and X.500.

29 Mar 2004