The Second Life client is also free/open source software (LGPLv2) [0]. There are multiple competing forks with significant user bases, the most popular of which

The Second Life client is also free/open source software (LGPLv2) [0]. There are multiple competing forks with significant user bases, the most popular of which is Firestorm [1]. The server software is closed source, but the OpenSimulator project [2] exists as a third-party reimplementation. [0] http://wiki.secondlife.com/wiki/Linden_Lab_Official:Second_Life_Viewer_Licensing_Program http://wiki.secondlife.com/wiki/Linden_Lab_Official:Second_L... [1] http://www.firestormviewer.org/ http://www.firestormviewer.org/ [2] http://opensimulator.org/wiki/Main_Page http://opensimulator.org/wiki/Main_Page