Orphaned packages have no active maintainer: they have
Maintainer: ORPHANED
in their DESCRIPTON file.

Orphaned packages remain in the main CRAN packages section as long as
they pass "R CMD check" for the current release version of R.

Everybody is more than welcome to take over as maintainer of an orphaned
package.  Simply download the package sources, make changes if necessary
(respecting original author and license!) and resubmit the package to
CRAN with your name as maintainer in the DESCRIPTION file of the
package.

Possible reasons for orphanizing a package:

1) The current maintainer actively wants to orphanize the package,
   e.g., due to no longer having time or interest to act as package
   maintainer.

2) Emails sent to the current maintainer by the CRAN admins bounced, or
   were not answered for longer periods of time.

The current orphanizing process:

1) File PACKAGES.in in CRAN's src/contrib directory (the repository
   package metadata file) adds a Maintainer: ORPHANED override and an
   X-CRAN-Comment entry providing information about the original
   maintainer, and the date and reason for orphanizing.

2) Package sources and binaries are updated on CRAN without increasing
   the version number.

3) If the package cleanly passes R CMD check for the current release
   version of R, it remains in CRAN's src/contrib directory.  Otherwise,
   it is moved to the Archive.