This directory contains a hand-made snapshot of what was the latest stable version at the time it was made.
You can also get a possibly more up-to-date version from SVN:
svn checkout svn://svn.code.sf.net/p/garnetlisp/svn/trunk garnetlisp-svn
garnetlisp-old contains old versions of Garnet.
tour.pdf and tutorial.pdf are from the excellent Garnet documentation. They will give you an idea of the features of Garnet and how it works.