There are several ways to get oxine:
If you are lucky your favorite distribution might have prepared a binary package. This should be the preferred way for nearly everybody.
If this is not the case you can always get the latest release from the sourceforge.net download area.
If you are interested in the very latest code (might be unstable and probably contains useless code) you can also get the source from subversion
svn co https://oxine.svn.sourceforge.net/svnroot/oxine/trunk/oxine
or by downloading the latest subversion-snapshot.
More information on how to use SVN can be found in the Subversion Manual.
Thanks to Sebastian Kemper you can download an ebuild that builds directly from subversion.