Get Active Caption

function ActiveCaption: string;
var
  Handle: THandle;
  Len: LongInt;
  Title: string;
begin
  Result := '';
  Handle := GetForegroundWindow;
  if Handle <> 0 then
  begin
    Len := GetWindowTextLength(Handle) + 1;
    SetLength(Title, Len);
    GetWindowText(Handle, PChar(Title), Len);
    ActiveCaption := TrimRight(Title);
  end;
end;

Beispiel :

procedure TForm1.Timer1Timer(Sender: TObject);
begin
  Label1.Caption := ActiveCaption;
end;