3store is an RDF "triple store", written in C and backed by MySQL and Berkeley DB. It is an optimisation and port of an older triple store (WebKBC). It provides access to the RDF data via RDQL or SPARQL over HTTP, on the command line or via a C API.
YARS is a data store for RDF in Java and allows for querying RDF based on a declarative query language, which offers a somewhat higher abstraction layer than the APIs of RDF toolkits such as Jena or Redland.
Jena is a Java framework for building Semantic Web applications. It provides a programmatic environment for RDF, RDFS and OWL, SPARQL and includes a rule-based inference engine.
A. Harth, und S. Decker. LA-WEB '05: Proceedings of the Third Latin American Web Congress, Seite 71. Washington, DC, USA, IEEE Computer Society, (2005)