Tupelo is a project to create a content repository to support data-driven scientific applications. More specifically it support JSR 170 (Content Repository API), WebDAV and URIQA (which are the extended HTTP verbs for getting RDF graphs). It implements a per object ACL and version control system.
It uses Kowari, 3Store, and Jena as backing stores. It also has a rather interesting API for dealing with triples called Context (more information in the cookbook). There are some smaller things too like using 1.5's varargs to add triples, transitive closures on queries, object to resource mapping and something that I'd meant to do for JRDF a while ago, have a ResourceVisitor that actually visits resources.
The presentation lists similar projects: SRB, Slide/SAM, Fedora, DSpace and Jackrabbit. All of which (except for SRB) I'm pretty familar with.
And ActiveRDF, a Ruby API for accessing RDF, went 1.0!