AD/AM is is "Active Directory Application Mode". It is a Lightweight Directory Access Protocol (LDAP) directory service, based on Active Directory technology. You can run ADAM on Windows Server 2003, or on Windows XP SP2 Professional.
Apps can use ADAM as a directory store, without deploying a domain, or a domain controller.
You can run multiple instances of ADAM concurrently on a single machine, with different schema in each instance. Cool. ADAM shipped with WS2003.
The forthcoming release of Windows Server is called "Windows Server 2003 R2". It includes a bunch of stuff, including .NET v2.0 (and ASP.NET v2.0, which I mentioned previously), ADFS, and other features. Interestingly, it also includes a little update to ADAM, a tool called the
Active Directory Schema Analyzer.
This tool analyzes directories and provides all sorts of insights. What's really cool: it works with any LDAP source, so you can use it to analyze your Netscape / iPlanet / SunOne Directory Server, IBM SecureWay, or openLDAP.
This ADSchemaAnalyzer tool is a no-cost part of Windows.