procedure TForm1.Button1Click(Sender: TObject);
var
  Wnd: hWnd;
  buff: array[0..127] of Char;
begin
  ListBox1.Clear;
  Wnd := GetWindow(Handle, gw_HWndFirst);
  while Wnd <> 0 do begin {Не показываем:}
    if (Wnd <> Application.Handle) and {-Собственное окно}
      IsWindowVisible(Wnd) and {-Невидимые окна}
      (GetWindow(Wnd, gw_Owner) = 0) and {-Дочернии окна}
      (GetWindowText(Wnd, buff, sizeof(buff)) <> 0) {-Окна без заголовков}
      then begin
      GetWindowText(Wnd, buff, sizeof(buff));
      ListBox1.Items.Add(StrPas(buff));
    end;
    Wnd := GetWindow(Wnd, gw_hWndNext);
  end;
  ListBox1.ItemIndex := 0;
end;