Are you looking for a free alternative for a Windows based Active Directory controller? The recently published version 4 allows Samba to be an Active Directory domain controller, participating fully in a Windows Active Directory Domain. This is a great replacement for a Windows based AD Controller if you want to use Active Directory features in your Lab.
With the new release of the Univention Corporate Server 3.1 (UCS) you can deploy your Samba 4 Controller in a few minutes. The quickest way is to use the preinstalled VMware Images.