Chin Huang observes that Microsoft's Active Directory Services Interface (ADSI) exposes a COM interface, so it is accessible through such examples as
# 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.