get the Active Window 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;

{ - - - - - - - - - - - - - - - - - - - - -}

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