The current stable release is Sozi 16.02 (February 2016):
Sozi is currently provided in the form of a zip archive.
Unzipping the archive will create a folder with the same name.
Linux and Windows users will run Sozi by launching the
Sozi executable inside that folder.
OS X users will find a
Sozi.app subfolder that they can drag into their
Sozi 13.11 is still available if you need it, but it is no longer maintained: