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.
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.
4store is an efficient, scalable, and stable RDF database. It was developed to underpin Semantic Web applications. It has been providing a base platform for these applications for around 3 years. It has successfully held and run queries over databases of 15GT, supporting a Web application used by hundreds of thousands of people.
Protégé provides a suite of tools to construct domain models and knowledge-based applications with ontologies. At its core, Protégé implements a rich set of knowledge-modeling structures and actions which support the creation, visualization, and manipulation of ontologies in various representation formats. It can be customized to provide domain-friendly support for creating knowledge models and entering data, and can be extended by way of a plugin architecture and a Java-based API for building knowledge-based tools and applications.