ShareJS is an Operational Transform library for NodeJS & browsers. It lets you easily do live concurrent editing in your app.

MVC framework making it easy to write realtime, collaborative applications that run in both Node.js and browsers.

In these 2 tutorials hallsofvallhalla teach us to deploy and use Socket.io to build Realtime communication accross the network, to sync the players and the server.

In this article, you will learn how to use Bogart and CouchDB to create a minimal blogging engine.

A Sinatra-Inspired JavaScript Framework running on JSGI

NowJS creates a magic namespace "now", accessible by server and client
Functions and variables added to now are automatically synced, in real-time
Call client functions from the server and server functions from client

Socket.IO aims to make realtime apps possible in every browser and mobile device, blurring the differences between the different transport mechanisms. It's care-free realtime 100% in JavaScript.