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.