Redland is a set of C libraries providing a high-level API for the Resource Description Framework (RDF), allowing it to be stored, parsed, serialized, queried, and manipulated. It has an object-based, modular design and comes with detailed reference documentation and examples. Redland supports all RDF vocabularies such as FOAF, RSS 1.0, Dublin Core, DOAP, and OWL, the query languages SPARQL and RDQL, and all RDF syntaxes including Turtle, RDF/XML, RDF/JSON, RSS, Atom, RDFa, and GRDDL.
Sesame is an Open Source RDF Schema-based repository and querying facility. It is a scalable, modular architecture for persistent storage and querying of RDF and RDF Schema. It supports two query languages (SPARQL and SeRQL), and can use main memory or PostgreSQL, MySQL and Oracle 9i databases for storage.
Rasqal is a C library for querying RDF graphs, supporting the SPARQL, RDQL, and LAQRS languages. It provides APIs for creating a query and parsing query syntax. It features pluggable triple-stores and matching interfaces, query engines for executing the queries, an API for manipulating results as bindings, and multiple ways to format the results to XML, CSV, TSV, and JSON. It uses the Raptor RDF parser to return triples from RDF content, and can alternatively work with the Redland RDF library's persistent triple stores. It is portable across many POSIX systems.
Soprano (formerly known as QRDF) is a library that provides a highly usable object-oriented C++/Qt4 framework for RDF data. It uses different RDF storage solutions as backends through a simple plugin system. Soprano is targetted at desktop applications that need a RDF data storage solution. It has been optimized for easy usage and simplicity.
Nx2 is a somewhat complex Web application that acts as a frontend to music databases. Based on XUL, it runs in Gecko based browsers such as Firefox. Built on this idea is a client/server model where several Nx2 frontends can connect to each other, creating a way to link together databases on different networks.
Graffiti is an RDF store based on dynamic translation of RDF queries into SQL. It allows you to map any relational database schema into RDF semantics and vice-versa, and to store any RDF data in a relational database. Since 2003, this RDF store was used as the primary means of data access in the Samizdat open publishing engine, and now it's released as a stand-alone module ready for use in other applications.
FDRDF is a tool that builds a catalogue of descriptions in an RDF representation of the specified files. The descriptions currently include: file status (as per the stat system call); SHA-1 hash over the file contents; MIME type (as guessed by the file tool), geospatial metadata (as per GDAL), and GRIB file composition (as per GRIB API).