For some context:

  54     clients.each(function(c) {
  55       if (c != client)
  56         c.connection.send(client.name + ": " + data);
  57     });

Line 55 is just there as a check to prevent echoing back the message to the client that sent it (as presumably the message they type will already be on their screen/terminal, if they are connected with netcat as the author suggests).