Samba can be configured to run as a domain controller and openldap is used as a database backend to samba and LAM is just there to make things easier with to integrate the two together with a web interface.

Name: Samba

HomePage: http://www.samba.org/

Function: Samba is a suite of programs that enables interoperability between Linux/Unix servers and Windows client

Name: OpenLDAP

HomePage: http://www.openldap.org/

Function: OpenLDAP is an open source implementation of the Lightweight Directory Access Protocol

Name: LAM (ldap account manager)

HomePage: http://lam.sourceforge.net/

Function: LDAP Account Manager (LAM) is a webfrontend for managing accounts stored in an LDAP directory.