You could also look at Badumna www.scalify.com
Badumna uses a hybrid of a peer-to-peer architecture and client-server. All state synchronization can be done peer to peer, removing the need for sharding and providing almost unlimited number of clients with real-time interaction. Functions that need to be done securely can stay client-server.
Edited by scalify, 27 September 2012 - 06:41 PM.