It would appear that www.BSurfaces.info the web site for the retopologizing tool has gone down and was gobbled up by a dentistry practice. Where is the project living now? Has someone put the code on Github? I can't seem to find it.
Even though the site is gone we still have the addon. In fact it comes with the default blender. Just search in the addons for bsurfaces. Or if you are looking for the code go to the addon folder in the blender directory
There are still a few places to get info about Bsurfaces.