Singularity Viewer is one of the viewers in the third party viewer directory. This page contains the reviews I’ve made of it.
Singularity Viewer was based on Snowglobe 1.5 code. It requires SSE2 support. If your computer is a a pre-2001 Pentium 4 vintage, it probably does not support SSE2. Some say it needs to be a 2004 vintage computer or newer. One can check by using a free little program named CPU-Z.
The viewer has now adopted code from the SL Viewer version 3 and is one of the more popular viewers in Second Life.
An unusual default setting in Singularity viewer is to have RLV (Restrained Life Viewer – a feature that allows the viewer to be programmed by in-world scripts) enabled by default.