This is a Plone product (that could probably be
trivially modified for the CMF itself) which
provides Atom support for Plone. Currently it
provides the Atom syndication format for folderish
objects, in the same way as RSS syndication is
implemented.
Railroad is a standards-based repository for large
binary files such as digital media, along with
their metadata. It is designed to be easy to
integrate with content management systems and
other client software.