EON is released under the GNU General Public License version 3.
A read-only copy of the code can be anonymously checked out of the subversion repository with the following command:
svn co http://theory.cm.utexas.edu/svn/eon
If you are a developer you should checkout the code like so:
svn co svn+ssh://email@example.com/svn/eon
This will fetch a copy of the latest code to a local directory named eon. For more information on subversion read its online documentation.