[lmikle]

Код просто поправил, логику не проверял:

Код:

unit Unit1;
 
interface
 
uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Vcl.ExtCtrls;
 
type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
  public
end;
 
var
  Form1: TForm1;
  n: Integer;
 
implementation
 
{$R *.dfm}

function EnumWindowsProc(wHandle: HWND; Param: Pointer): BOOL; stdcall;
var
  Title, ClassName: array[0..255] of char;
begin
  GetWindowText(wHandle, Title, 255);
  GetClassName(wHandle, ClassName, 255);
  if IsWindowVisible(wHandle) and (ClassName = 'TForm8')
  then begin
       Inc(n);
       SetWindowText(wHandle, Format('Кукарямба %d', [n]));
       end;
  Result := True;
end;
 
procedure TForm1.Button1Click(Sender: TObject);
begin
  n := 0;
  EnumWindows(@EnumWindowsProc, 0);
end;

end.