tar.gz is a type of zipped folder archive. Perhaps it could be a little more clear.
Update packages (and most everything else) are usually distributed inside .zip archives, but some people prefer more efficient compression. tar.gz is not quite so common in the Windows world.
Use
7-Zip and you can extract it. Alternatively, download the latest zip from the GitHub code repository linked there, and copy the librariansync folder into "extensions".