What simple AtomPub server libraries with file- or DB-based backends can you recommend? Unix-style servers that "do one thing, do it well" are especially welcome.
Maybe even libraries in Python?
Maybe this?
http://atomserver.codehaus.org/
If someone is looking for a library to use in building Atompub into an existing service, they should definitely use Abdera directly. AtomServer, by contrast, is a full java web application that can be up and running in a few minutes by configuring a database and a few XML configuration files. It addresses all of the metadata and content management pieces that Abdera doesn't, and it's undergone a lot of battle-hardening to make it rock-solid and performant. Our goal moving forward is to make AtomServer easily interoperable with any spec-compliant Atom Client, while making the deployment of a server as easy as possible, with as little coding as possible.