Class KACL
    Friend GrpName As String
    Friend Members As New List(Of String)
 
    Sub AddMembers(ByVal _NewMember As String)
        Members.Add(_NewMember)
    End Sub
End Class

Dim LiKacl As New List(Of KACL)

'Abfrage
Dim Q = From x In LiKacl, m In x.Members
        Group x By m Into Group
 
'Ergebnisse
For Each x In Q
  Dim Member As String = x.m 'Alle vorkommenden Member
  Dim Gruppen As IEnumerable(Of KACL) = x.Group 'Alle Gruppen mit diesem Member
Next