A basic chat server written in Node.js. Tried to improve on the ones that are currently floating around. Note: Not great from telnet on Windows - works fine on *nix.

ChatServer.js

/*
    File: ChatServer.js
    Author: Nerdwaller
    Description:
        A fairly simple chat server using Node.js.  
        It takes several pieces from other scripts, adds some original pieces, and additional functionality.
*/
var net = require("net");

// Server Config
var SERVER = {
    name : "Node.js Simple Chat Server",
    port : 8000,
    host : "127.0.0.1",
    prmpt: "> "
};

// Class For Client Sockets
function Socket(socket) {
    this.uname = null;          // Username
    this.id = null;             // Unique ID (IP:PORT)
    this.socket = socket;       // Socket Object
    this.buffer = "";           // Buffer of Text
}

// Proto for removing items from arrays.
Array.prototype.remove = function(e) {
    for (var i = 0; i < this.length; i++) {
        if (e == this[i]) {
            return this.splice(i, 1);
        }
    }
};
// Proto to check for an object in the array (Searches by member variable)
Array.prototype.exists = function(attrib, value) {
    var found = false;
    this.forEach(function(c) {
        if (c.hasOwnProperty(attrib) && c[attrib] == value) {
            found = true;
        }
    });
    return found;
};

// List of connected clients
var CLIENTS = [];

// Create the server and add listeners for events.
var srv = net.createServer(function(socket) {
    // CTOR (Client Connect)
    var client = new Socket(socket);
    CLIENTS.push(client);
    socket.setEncoding("utf8");
    client.id = socket.remoteAddress + ':' + socket.remotePort;
    client.uname = client.id; // Set a default username
    // Report to the server and other clients that someone has connected.
    console.log("+" + client.id + ", " + CLIENTS.length + " connected clients.");
    socket.write("Welcome to " + SERVER.name + ".\r\n");
    socket.write(SERVER.prmpt);
    CLIENTS.forEach(function(c) {
        if (c != client) {
            c.socket.write("\r<srv>: " + client.id + " has joined.\r\n");
            c.socket.write(SERVER.prmpt);
        }
    });

    // DTOR (Client Disconnect)
    socket.addListener('end', function() {
        CLIENTS.remove(client);
        console.log("-" + client.id + ", " + CLIENTS.length + " connected clients.");
        CLIENTS.forEach(function(c) {
            c.socket.write(client.id + " has left.\r\n");
            c.socket.write(SERVER.prmpt);
        });
        socket.end();
    });

    // Handle Received Data
    socket.addListener("data", function(d) {
        client.buffer += d;
        if (client.buffer[client.buffer.length - 1] == "\n") {
            if (client.buffer.match(/^!.*/)) { // A command always takes form !command
                var cmd = client.buffer.split(" ")[0];
                var params = client.buffer.split(" ");
                cmd = cmd.replace("!", "").trim();
                switch(cmd) {
                    case "quit":
                        client.socket.end();
                        return;
                    case "set":
                        switch(params[1]) {
                            case "name":
                                if (!CLIENTS.exists("uname", params[2].trim())) {
                                    client.uname = params[2].trim();
                                }
                                else {
                                    client.socket.write("Username already taken.\r\n");
                                }
                                break;
                            default:
                                client.socket.write("Valid !set commands:\r\n\t!set name uname\r\n");
                        }
                        break;
                    default:
                        client.socket.write("Invalid command.\r\n");
                }
            }
            else {
                CLIENTS.forEach(function(c) {
                    if (c != client) {
                        c.socket.write("\r" + client.uname + ": " + client.buffer);
                        c.socket.write(SERVER.prmpt);
                    }
                });
            }
            client.buffer = "";
            client.socket.write(SERVER.prmpt);
        }
    });

    // Interrupt Handlers
    process.on('SIGINT', function() {
        console.log("SIGINT detected, shutting down server and disconnecting all clients (" + CLIENTS.length + ").");
        CLIENTS.forEach(function(c) {
            c.socket.write("Server is shutting down, your connection will be closed.");
            c.socket.end();
        });
        process.exit();
    });
});

srv.listen(SERVER.port, SERVER.host);
console.log("Server is running on " + SERVER.host + ":" + SERVER.port);