procedure TForm1.AppDeactivate(Sender: TObject);
var
  hw: HWnd;
  CurTask: THandle;
  WndStyle: Longint;
begin
  CurTask := GetWindowTask(handle);
  hw := GetWindow(GetDesktopWindow, GW_CHILD);
  while GetWindowTask(hw) <> CurTask do
    hw := GetWindow(hw, GW_HWNDNEXT);
  while (hw <> handle) and (GetWindowTask(hw) = CurTask) do
  begin
    PostMessage(hw, WM_Close, 0, 0);
    hw := GetWindow(hw, GW_HWNDNEXT);
  end;
end;