function EnumWindowsProch(Wnd : HWnd;Form : TForm1) : Boolean;
Export; {$ifdef Win32} StdCall; {$endif}
var
Buffer : Array[0..99] of char;
begin
GetWindowText(Wnd,Buffer,100);
if StrLen(Buffer) <> 0 then
form1.listbox1.items.Add(StrPas(Buffer));
Result := True;
end;

function EnumWindowsProc (Wnd: HWND; LParam: LPARAM): BOOL; stdcall;
Var Title : PChar;
begin
Result := True;
if (IsWindowVisible(Wnd) or IsIconic(wnd)) and
((GetWindowLong(Wnd, GWL_HWNDPARENT) = 0) or
(GetWindowLong(Wnd, GWL_HWNDPARENT) = GetDesktopWindow)) and
(GetWindowLong(Wnd, GWL_EXSTYLE) and WS_EX_TOOLWINDOW = 0) then
begin
Title:=StrAlloc(255);
GetWindowText(Wnd,Title,255);
form1.listbox1.items.add(StrPas(Title));
//ShowMessage(StrPas(Title));
StrDispose(Title);
end;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
listbox1.items.clear;
EnumWindows(@EnumWindowsProc,0);
end;