If Second Life needs to evolve even further there is no way around Open Source. Therefore Linden Lab decided to release the Client Code and they are working on a release of the server code. Of course Accident Designs are looking forward to the release and we expect it will enable us to set up our own exclusive servers available for our customers.
Open source virtual worlds already exist but the release of the Second Life source code will definitely bring us closer to a 3d network accessible to the whole world as we know it with WWW.
Know more:Open Source Busybody Reporting for Duty - Official Linden Blog
Embracing the Inevitable - Official Linden Blog
http://www.opencroquet.org/ - 2 existing open source virtual worlds