If you run into a situation, where you would like to create and show a form, but you know the class's name only, you need to use the functions FindClass:
procedure ShowAnyForm(sFormClassName: string);
var
FormClassType: TFormClass;
Form: TForm;
begin
// possibility #1 FormClassType := TFormClass(FindClass(sFormClassName));
Application.CreateForm(FormClassType, Form);
Form.ShowModal;
Form.Free;
// possibility #2 Form := TForm(TComponentClass(FindClass(sFormClassName)).Create(Self));
Form.ShowModal;
Form.Free;
end;