Link: http://www.ontologyportal.org
Source Author or Organization: Adam Pease

The Suggested Upper Merged Ontology is a free, formal upper ontology, expressed in first order logic, and in OWL/XML. It has been mapped to all of the WordNet lexicon, dozens of free domain-specific ontologies have been created from it, an open-source browser is available and format files supplied with the browser allow logic statements to be presented in English, Hindi, Chinese, Italian, German and Czech as well as logic. SUMO has also been subjected to formal consistency checking with first order logic theorem provers.