I came across an old wiki page that is getting new updates. Rob Linden started the page in 2006. For the last few months Oz Linden and Wolfpup Lowenhar have been updating the page almost weekly. If you are interested in what is going on in viewer development, you may find the page interesting.
You can get versions of development viewers made by the Snowstorm Team and TPV Developers.
Be warned that these viewers may have more or less problems than the current stable release of the SLViewer or related TPV.
The Snowstorm download on the ‘test builds’ page seem to the the same link found on the Snowstorm Project page.
The latest Snowstorm Development Viewer is: Second Life 3-1-1-242785 Development.