Version 12 of ADSI

Chin Huang observes [L1 ] that Microsoft's Active Directory Services Interface (ADSI) [L2 ] exposes a COM interface, so it is accessible through such examples as using tdom

    # List all users in the domain named "MAIN".
    package require tcom

    set domain "MAIN"
    set collection ::tcom::ref getobject "WinNT://$domain"
    $collection -set Filter list "User"
    ::tcom::foreach item $collection {
        puts $item Name
    }

Also, Franco Violi's TclLDirectory extension is said to understand ADSI.

Yet another way to consider Active Directory is as an instance of LDAP service.

More ADSI-Examples can be found at Matthias Hoffmann - Tcl-Code-Snippets (not yet complete but growing...)