Lincoln Mullen, PhD candidate at Brandeis University, has created the Catalog Search plugin for Omeka, which builds upon Omeka’s Library of Congress Subject Heading plugin to search Archive Grid, the DPLA, Google Books, Google Scholar, the Hathi Trust, JSTOR, the Library of Congress, and WorldCat based on subject heading. See it in action at the American Converts Database (example) and see the code on GitHub.
