Public Class Form1
    Declare Function GetForegroundWindow Lib "user32" () As IntPtr
    Declare Auto Function GetWindowRect Lib "User32" (ByVal hWnd As IntPtr, _
      ByRef lpRect As Rect) As Int32
 
    Public Structure Rect
        Public Left As Int32
        Public Top As Int32
        Public Right As Int32
        Public Bottom As Int32
    End Structure
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles MyBase.Load
        NotifyIcon1.Icon = Me.Icon
    End Sub
 
    Private Sub NotifyIcon1_MouseMove(ByVal sender As Object, ByVal e As _
      System.Windows.Forms.MouseEventArgs) Handles NotifyIcon1.MouseMove
        Dim r As New Rect
        GetWindowRect(GetForegroundWindow, r)
        Dim re As New Rectangle(r.Left, r.Top, r.Right - r.Left, r.Bottom - _
          r.Top)
        NotifyIcon1.Text = "Aktives Fensters: " & re.ToString
    End Sub
End Class