Swoogle describes itself as being the search engine for the Semantic Web. Swoogle crawls the web looking for RDF documents. At this time Swoogle offers the these services:

• Search ontologies and instance data
• Search terms (URIs that have been defined as classes and properties)
• Provide metadata of Semantic Web documents
• Support browsing the Semantic Web
• Archive different versions of Semantic Web documents

Who's behind Swoogle?

Straight from the source:

Swoogle is a research project being carried out by the ebiquity research group in the Computer Science and Electrical Engineering Department at the University of Maryland, Baltimore County (UMBC). Partial research support was provided by DARPA contract F30602-00-0591 and by NSF by awards NSF-ITR-IIS-0326460 and NSF-ITR-IDM-0219649. Contributors include Tim Finin, Li Ding, Rong Pan, Anupam Joshi, Pavan Reddivari, Joel Sachs, Pranam Kolari, Akshay Java, Lushan Han, Yun Peng, R. Scott Cost, Sandor Dornbush and Vishal Doshi.

Swoogle for developers

Developers will be interested to know that Swoogle offers its service through a REST interface and notes that their entire Website is based on this service.