I don't know what part or aspect of SL you think couldn't have been done Open Source, but there was this company called Nevrax who developed and launched this M

I don't know what part or aspect of SL you think couldn't have been done Open Source, but there was this company called Nevrax who developed and launched this MMO called Ryzom. It was not a commercial success, but it got done, and it was open sourced all along, which AFAIK did't hurt them much. Edit: http://www.fsf.org/news/free-ryzom http://www.fsf.org/news/free-ryzom (where it also says Linden Labs has GPLed the client code for Second Life, back in 2007.)