source code of http://atom2rss.appspot.com/
A web aplication can converts atom 1.0 feed into an RSS2 feed.
1: only can convert atom 1.0 to rss 2.0
2: written with jython+modjy
3: can run on GoogleAppEngine or some other java servlet containers
4: use the atom2rss.xsl file from http://atom.geekhood.net/