The is a distribution of Org-mode, a plain text notes and project planning
tool for Emacs.
The homepage of Org-mode is at http://orgmode.org
The manual is in the file org.pdf, it includes a section about installation.
The xemacs directory contains special code for XEmacs users, in particular
a port of the GNU Emacs outline.el to XEmacs.  Org-mode does not work
under XEmacs without this file installed.  It did until version 4.37,
but no longer.
If this is the git project, there are additional directories here:
CONTRIB
    contains bits and pieces contributed by users.  These are not yet
    part of the Org-mode core, and also not part of Emacs.
EXPERIMENTAL
    files that contain code bits for experimenting.  Nothing has been
    decided on what to do with these.