Many applications can make good use of Microsoft's Active Directory service. Up until recently Microsoft required the Active Directory to be installed on a domain server, and this most often was not the server that the application ran on. Locating AD on another system both imposed a performance penalty, and restricted the ability of developers to modify AD for specific application use.
The Active Directory Application Mode or ADAM was developed to address these issues. ADAM is a component of Windows Server 2003 that also can be installed on Windows XP Professional. There are versions of ADAM for Windows Server 2003 Standard, Enterprise and Datacenter Edition. That includes both the 32-bit versions of Enterprise and Datacenter server, and both versions of XP Professional SP 1. ADAM runs as a separate service apart from the Windows OS. Each instance of ADAM supports a single application, but you can run multiple instances on the same server if you need to.
From a developers' point of view, ADAM supports APIs such as LDAP, ADSI (Active Directory Interface), and the DSML (Directory Services Markup Language), all transparently interoperable with a full implementation of AD. This allows any application built on ADAM to be transferred to AD at a later date. ADAM can be installed on a domain controller, domain member or a workgroup member, and doesn't require you to create a domain or forest to support it.
Download instructions may be found here; which depending upon the version you download runs from 8.5 to 34.7 MB.
Barrie Sosinsky is president of consulting company Sosinsky and Associates (Medfield MA). He has written extensively on a variety of computer topics. His company specializes in custom software (database and Web related), training and technical documentation.