Elias Torres, Wing Yung and Ben Szekely have created an ATOM-Server called Queso with a little interface using AJAX:

Queso is a J2EE-style application that implements the Atom Protocol specification currently in draft-09 atop an RDF server called Boca (the restaurant’s name is Boca Grande, a.k.a. Big Mouth) using Henry Story’s Atom OWL for the model and of course opening up a SPARQL endpoint to query the contents the store.

The actual data-storing takes place using RDF-Data. But the data is inserted by the user or the machine using Atom-syntax:

Content is inserted into the system is by posting Atom entries. The entries are stored as RDF (converted via Atom OWL by Henry Story), so their content and metadata is accessible via SPARQL queries. []

But test yourself under http://abdera.watson.ibm.com:8080/browser/. Its very rudimental so far, but looks promising.