[This API is no longer available and this page is being maintained purely for historical and research purposes.]
Ontos is a provider of tools that aggregate content that is semantically related to content that already exists on a website or blog. Their API returns semantic metadata in RDF-based formats for existing text content. The API uses natural langugage processing to recognize entities and the relations between them. With the API, uses can link their text content with metadata coming from over 500,000 web documents. Full documentation is not publicly available.