In mid 2011, "Kirstens Viewer" based on Linden Labs' open source Second Life Viewer code, added support for 3D stereo vision using a variety of 3D methods, including simple red/cyan glasses.  This viewer is no longer maintained and is not available for download.  but the last version created - Kirstens S21(9) - still works with current Second Life servers. Here is an example image from Kirtsen's Viewer in red/cyan 3D (click on image for a full sized copy and get out your 3D glasses to see the effect):

There was an earlier patch for an early version of  the Second Life Viewer from the University of Michigan to support 3D stereoscopic views in Second Life. See http://3dvision-blog.com/forum/viewtopic.php?f=2&t=142 and https://jira.secondlife.com/browse/VWR-2972?