The Google FeedServer is an open-source Atom Publishing provider based on the
Abdera Framework. Google FeedServer implements simple backend data
adapters that allow the developer to quickly deploy a feed for an existing
data source such as a database. The FeedSever makes it easy to create these
adapters.

The home of the project is at:

http://code.google.com/p/google-feedserver/

There, you'll find links to Abdera as well as more reading material in the Wiki.
For example, an overview of the project is at:

http://code.google.com/p/google-feedserver/wiki/Overview