While the simpler of the two architectural components (core and connector), the Jangle core has the distinction of being public face of Jangle and therefore the only part of Jangle that most people should ever have to see.
The core, in essence, is an Atom Publishing Protocol proxy to the registered backend connectors. It routes the HTTP requests to the connectors, and serializes the JSON responses to Atom feeds.
There is one reserved path, /services/, which returns the Atom Service Document defining the registered connectors. Any internal Jangle core resources (such as users/authentication) would also be defined in this service document.
Example:
<?xml version="1.0" encoding="UTF-8"?>
<service xmlns="http://www.w3.org/2007/app" xmlns:atom="http://www.w3.org/2005/Atom">
<workspace>
<atom:title>openbiblio</atom:title>
<collection href="http://anvil.lisforge.net:6767/openbiblio/actors"/>
<atom:title>patrons</atom:title>
<accept>text/x-vcard</accept>
<accept>text/directory;profile=vcard,text/directory</accept>
<collection href="http://anvil.lisforge.net:6767/openbiblio/resources"/>
<atom:title>Catalog records</atom:title>
<accept>application/marc21</accept>
<accept>application/marc21+xml</accept>
</workspace>
</service>
What you see here is a Jangle core set up with a single connector. Connectors are defined in the service document as a "workspace". The resources exposed by the connectors (Actor, Resources, Items, etc.) are "collections" in the atom service context.
The core must also be able to assign absolute URLs to the resources exposed and provide persistence to the resource URIs (including providing 410 or 404 responses to resources that have been permanently deleted). This way it's possible to put Jangle defined URIs for other services with some confidence in your metadata.
This goal of this project is to provide at least one working Jangle core implementation (currently found in the Google code subversion repository), but also be simple to use off the shelf AtomPub servers, such as Apache's Abdera or amplee (although they would need adapters to speak Jangle connectors).