"Microsoft has made an investment into that technology by rewriting MIIS pretty much from scratch. And Siemens to this date probably has the most comprehensive and advanced meta-directory implementation with its DirXmetahub component that is part of its Dir-X offering. Nevertheless, meta-directories are arguably still around mostly because Microsoft forces this technology onto its customers for what I think are political reasons: Several people working for Microsoft in the field have told me that is was in Microsoft’s interest to have Active Directory as a central component, and believe it against Microsoft’s interest to have a “filtered access”, such as a virtual directory in front of AD, abstracting information away from what should be the authoritative source. I never really understood this fear, but recently it seems that this brick wall may be slowly starting to crumble."