Thank you for the link @groundFungus .
I understand what is meant with "easy set up and use".
And I have seen, it is a direct transmission on a very low level.
That may be a good solution for simple transfer of a few bytes as @StefanL38 wants to have.
For me it would not fit, because it seems to run only with ESPs. Wonder if you can use a DUE (or other Arduinos) with WiFi-Shield or even transfer data to Your Smartphone or Notebook/PC, which is nearly the same interface when using sockets. Of course You need a router (access point) with UDP and a mixture of devices like arduinos, computers, tablets and smartphones.