Company
Microforte was at the Game Developers' Conference a few days ago where they were showing off their Big World Technology.. Gamespot has an article on what Big World can do!
"The engine can support up to 4 million players and doesn't require sharding--breaking up the gameworld into separate servers--except in ways that developers find necessary for gameplay reasons. The world doesn't require any zoning and can seamlessly transition from exterior to interior environments. The server technology is said to be very stable and has been complete since last year"