These are Windows compiled html files for the CGNS documentation.
Note: After downloading to Windows, you may have to right-click on the
file to bring up the Properties menu and click on Unblock in order
to be able to use it.
There are numerous programs available for viewing the CHM files
on other systems besides Windows. Some of these (available on
SourceForge) are GnoCHM, CHM Reader (Firefox extension), kchmviewer
and xCHM. I can not comment on any of these, since I have only used
an old version of GnoCHM on Fedora 9 Linux.