"A year has passed since Linden Lab, maker of the popular 3-D
virtual world Second Life, released the source code to its Second
Life viewer under the GNU GPL. In that time, a viable community of
developers has grown up around the SL code, and the company is
pleased enough with the success that it has branched out further
into open source and open standards.
"The SL viewer code was released on January 8, 2007, and has
spawned multiple unofficial offshoots. Most of the unofficial
viewers listed at the SL wiki are individually maintained and focus
on adding specific features. Some add or enhance existing features
such as the particle system, some integrate bug fixes not yet
rolled out to the official viewer, and some even roll back changes
made in the official viewer..."