Get the source tarball there: ssr-0.6.1.tar.gz
If you have a Mac, you can install the SSR with Homebrew:
brew install SoundScapeRenderer/ssr/ssr
There is also a Debian package available (thanks to IOhannes m zmoelnig): https://packages.debian.org/soundscaperenderer
An experimental (and not feature-complete) version for MS Windows is available at https://github.com/chris-hld/ssr.
If you are interested in older releases, check out all downloads.
You should also have a look at the development pages at Github: http://github.com/SoundScapeRenderer/ssr.