RDF

Semantic filters and layers over a semantically marked up document.
This module is an extension for the Semantic Markup Editor module: http://drupal.org/project/semantic_markup_editor You can create filters to semantic information and attach style layers to filters.

1. Multiple Systems of Units
2. Comprehensive Coverage of Quantities
3. Ontology Support for Units Conversion using Dimensions
4. Simple and Structured Data Types

The RDF SPARQL Endpoint module indexes the RDF data publicly available on a Drupal site into an ARC2 RDF store. It also provides a SPARQL endpoint via the ARC2 SPARQL interface.

SPARQL, RDF, and XQuery, XML -- this specification merges both in the novel language XSPARQL that "has the potential to finally bring XML and RDF closer together. XSPARQL provides concise and intuitive solutions for mapping between XML and RDF in either direction, addressing both the use cases of GRDDL and SAWSDL. As a side effect, XSPARQL may also be used for RDF to RDF transformations beyond the capabilities of "pure" SPARQL".

RDF vocabularies / ontologies available in RDFS and OWL formats.

Pointed out by Mike Anello during my DrupalEasy interview.