SocketCluster – A scalable realtime engine for Node.js
github.com
github.com
It looks like SocketCkuster does this plus add another layer of managed load-balancing and handshaking, i.e it's designed around being clustered rather than socket.io which seems to be designed for single server.
I'd love to hear if this is correct and see some performance comparisons of SocketCluster vs Socket.io configured similarly (as above).