Закрыть все окна

Function EnumWindowsFunc(Wnd: HWND; Param: LPARAM): BOOL; Stdcall;
Var
  Control: TControl;
Begin
Result := True;
If IsWindow(Wnd) Then
  If IsWindowVisible(Wnd) Then
    Begin
    Control := TControl(Param);
    If Assigned(Control) And (Control Is TMemo) Then
      (Control As TMemo).Lines.Add('#' + IntToHex(Wnd, 8));
    End;
End;
 
Procedure TForm1.Button1Click(Sender: TObject);
Begin
EnumWindows(@EnumWindowsFunc, LPARAM(Memo1));
End;

Function GetCaption(Wnd: HWND): String;
Var
  Len: Integer;
  ErrorCode: DWORD;
Begin
Len := 256;
SetLength(Result, Len);
Len := GetWindowText(Wnd, PChar(Result), Len);
If (Len = 0) Then
  Begin
  ErrorCode := GetLastError();
  If (ErrorCode = S_OK) Then
    Result := ''
  Else
    Result := SysErrorMessage(ErrorCode); // RaiseLastOSError(ErrorCode);
  End
Else
  Begin
  SetLength(Result, Len);
  End;
End;
 
Function EnumWindowsFunc(Wnd: HWND; Param: LPARAM): BOOL; Stdcall;
Begin
Result := True;
If IsWindow(Wnd) Then
  If IsWindowVisible(Wnd) Then
    If GetCaption(Wnd) = 'Калькулятор' Then
      PostMessage(Wnd, WM_CLOSE, 0, 0);
End;