"SKOSEd is a plugin for Protege that allows you to create and edit thesauri (or similar artefacts) represented in the Simple Knowledge Organisation System (SKOS)."
Triplify provides a building block for the "semantification" of Web applications. Triplify is a small plugin for Web applications, which reveals the semantic structures encoded in relational databases by making database content available as RDF, JSON or Linked Data.
Soprano (formerly known as QRDF) is a library which 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.
Cytoscape is an open source software platform for visualizing complex-networks and integrating these with any type of attribute data. A lot of plugins are available for various kinds of problem domains, including bioinformatics, social network analysis, and semantic web.
"Semantic Radar is a semantic metadata detector for Mozilla Firefox. It detects the presence of SIOC, FOAF and DOAP as well as generic RDF and RDFa data in a webpage, and displays icons in the browser's status bar when one of these data formats is found. By clicking on an icon the user can browse the RDF data in an online semantic browser. It looks for RDF auto-discovery links generated by data export plugins to discover semantic data."
Semantic Radar is a semantic metadata detector for Mozilla Firefox.
Available at Mozilla Add-ons site. It is a browser extension which inspects web pages for links to Semantic Web metadata and informs about presence of it by showing an icon in browser's status bar. Currently it supports RDF autodiscovery (SIOC, FOAF, DOAP and any type) and RDFa metadata detection.
New: Semantic Radar can now ping the Semantic Web Ping Service when metadata are detected. This allows for a community based discovery of the Semantic Web data.