S is for Schema

"The RDF Schema Specific Data Base (RSSDB) RSSDB (v1.5.1) is a persistent RDF Store for loading resource descriptions in an object-relational DBMS (ORDBMS) by exploiting the available RDF schema knowledge. It preserves the flexibility of RDF in refining schemas and enriching descriptions at any time, whilst it can store resource descriptions created according to one or more associated RDF schemas."

It supports string, integer, float, boolean and dateTime XML Datatypes. Just for a change it's using a Postgres backend. However, it doesn't support reified statements.

http://139.91.183.30:9090/RDF/RSSDB/index.html

A more impressive list of RDF Resources:
http://139.91.183.30:9090/RDF/references.html