Get all Open Windows

function EnumWinProc(Wnd: THandle; LParam: LongInt): Boolean; stdcall;
var
  WinCaption : string;
  Len: integer;
begin
  Result := True;
  Len := GetWindowTextLength(Wnd);
  SetLength(WinCaption, Len);
  GetWindowText(Wnd, PChar(WinCaption), Len+1);
  if Trim(WinCaption) <> '' then
    Form1.Listbox1.Items.Add(Format('%.6x : %s', [Wnd, WinCaption]));
end;

Beispiel :

procedure TForm1.FormCreate(Sender: TObject);
begin
  EnumWindows(@EnumWinProc, 0);
end;