I'm using port knocking on my routers. When I want to log in to router, first I have to knock using webbrowser http://my-router:3500
Could you add to winbox option called knock port. Before connect, first winbox will knock port.
Ah, you were looking for a client tool... I misundestood your question.
The best you can do is to make a script in your preferred language to knock an then invoke winbox (on the command line you can put address, user and password), or create a more complex gui yourself.