First of all, thank you for SFML! I just found out about this awesome library today, and I am loving it so much. So whether you contribute to the source code, or forum, or donate to this library, or just keeping it alive, thank you so much!
I have a minor suggestion on
http://www.sfml-dev.org/tutorials/2.3/network-socket.php today.
I really loved the outline on TCP vs UDP as I loved all other tutorials. It lists several differences, but it seems to me that the first one and the last one are the same.
The main difference is that TCP sockets are connection-based. You can't send or receive anything until you are connected to another TCP socket on the remote machine. Once connected, a TCP socket can only send and receive to/from the remote machine. This means that you'll need one TCP socket for each client in your application.
UDP is not connection-based, you can send and receive to/from anyone at any time with the same socket.
Oh, and one last thing: since UDP is not connection-based, it allows broadcasting messages to multiple recipients, or even to an entire network. The one-to-one communication of TCP sockets doesn't allow that.
BTW, all the tutorials go in depth to explain all things that aren't even central to SFML, so I really appreciate these. Thank you again!