XML::Atom::Syndication a simple lightweight client for consuming Atom syndication feeds. 0.02
XML::Atom::Syndication::Element a class representing a tag element in an Atom syndication feed with an XPath-esque interface.
Derived from Isofarro's atomrest.pl server and drawing heavily on Benjamin Trott's XML::Atom Perl module, I've written a subclass of the Perl module XML::Atom::Server. The goal is not to implement a complete server, but rather to provide a Perl module that others can subclass in order make a server. It's like XML::Atom::Server, but it provides more prepackaged functionality.
isoTopeis a web-based application framework built around Atom and the AtomAPI. It is designed to be modular and extensible. It is released under the GNU General Public License. Its only at version 0.1 - the very first version, and the code is rough (although a lot better than my first PHP implementation of the AtomAPI.
Sam Ruby has a quick-start guide for monitoring AtomAPI data transfer (or debugging anything else that uses http) with the tcpmon tool from Apache Axis. He also has a patch for Mark and Joe's API client which gives it proxy support.