Application.Handle

ServerApplicationHandle: = FindWindow ('TForm1', 'Form1');

var
  FW_ah, FW_mfh, ah, mfh: THandle;

  Procedure Display(OnTask: Boolean);
  begin
    Application.MainFormOnTaskbar := OnTask;
    ah := Application.Handle;
    mfh := MainForm.Handle;
    FW_ah := FindWindow(PChar(Application.ClassName), PChar(Application.Title));
    FW_mfh := FindWindow(PChar(ClassName), PChar(Caption));
    Showmessage(Format('ah: %d FW_ah: %d  -  mfh: %d FW_mfh: %d', [ah, FW_ah, mfh, FW_mfh]));
  end;

begin
  Display(true);
  Display(false);
end;