Private activeWindows As List(Of activeWindow)
''' <summary>Gibt alle geöffneten Fenster zurück.</summary>
    Public ReadOnly Property OpenWindows() As List(Of activeWindow)
        Get
            Return activeWindows
        End Get
    End Property

Private activewindows As List(Of Form1.activeWindow)
Private Sub AddRemoveWindows_Load(ByVal sender As System.Object, ByVal e As _
  System.EventArgs) Handles MyBase.Load
activewindows = Form1.OpenWindows
...