Active Directory Explorer is a Microsoft Utility that can be used to access the Active Directory of your company or your personal system so that you can check and navigate through your users. This can list all the domains, directories and users registered to each directories. You can also do search functionality and modifications.
Source : http://technet.microsoft.com/en-us/sysinternals/bb963907.aspx
You can download a mirror of the file here AdExplorer.