Qt::Tool not works as expected

#include <QApplication>
#include <QWidget>

int main(int argc, char **argv)
{
    QApplication app(argc, argv);

    QWidget window;
    QWidget *tool = new QWidget(&window, Qt::Tool);
    tool->setWindowTitle("I'm tool");
    tool->show();
    window.show();

    return app.exec();
}