Nodejs - módulo websocket-node:¿Cómo hacer que funcione el servidor de socket multicliente?

No está almacenando las conexiones en el lado del servidor. Simplemente los está configurando en el servidor para comunicarse directamente de ida y vuelta con el servidor. Si desea que los mensajes que van al servidor se envíen de vuelta a todos, debe configurar .on('message', ...) para que cada conexión en el servidor tenga ese comportamiento. Para hacer esto, deberá almacenar las conexiones a medida que se crean. Prueba esto:

var WebSocketServer = require('websocket').server;
var http = require('http');

var server = http.createServer(function(request, response) {
    console.log((new Date()) + ' Received request for ' + request.url);
    response.writeHead(404);
    response.end();
});
server.listen(5050, function() {
    console.log((new Date()) + ' Server is listening on port 5050');
});

wsServer = new WebSocketServer({
    httpServer: server,
    // You should not use autoAcceptConnections for production 
    // applications, as it defeats all standard cross-origin protection 
    // facilities built into the protocol and the browser.  You should 
    // *always* verify the connection's origin and decide whether or not 
    // to accept it. 
    autoAcceptConnections: false
});

function originIsAllowed(origin) {
  // put logic here to detect whether the specified origin is allowed. 
  return true;
}

//create an array to hold your connections
var connections = [];

wsServer.on('request', function(request) {
    if (!originIsAllowed(request.origin)) {
      // Make sure we only accept requests from an allowed origin 
      request.reject();
      console.log((new Date()) + ' Connection from origin ' + request.origin + ' rejected.');
      return;
    }
    var connection = request.accept('echo-protocol', request.origin);

    //store the new connection in your array of connections
    connections.push(connection);
    
    console.log((new Date()) + ' Connection accepted.');
    connection.on('message', function(message) {
        if (message.type === 'utf8') {
            console.log('Received Message: ' + message.utf8Data);

            //send the received message to all of the 
            //connections in the connection array
            for(var i = 0; i < connections.length; i++) {
                connections[i].sendUTF(message.utf8Data);
            }
        }
        else if (message.type === 'binary') {
            console.log('Received Binary Message of ' + message.binaryData.length + ' bytes');
            connection.sendBytes(message.binaryData);
        }
    });
    connection.on('close', function(reasonCode, description) {
        console.log((new Date()) + ' Peer ' + connection.remoteAddress + ' disconnected.');
    });
});