The General SPARQL app lets you navigate the semantic web using an extensible set of pre-defined queries. You can start from a single entity of interest (such as a protein) and expand the network. The app is pre-configured to visualise public data from Reactome, Uniprot, HGNC, NCBI Taxonomy, Chembl and other public resources. The app can be extended to work with any public or private RDF resource. The app is an open source contribution from [http://www.generalbioinformatics.com/ General Bioinformatics], available under GPL v2.
Watch the screencast at http://goo.gl/v6Djyo
See also the official [http://generalbioinformatics.github.io/general-sparql-cy3/ General SPARQL] website