Opensearch3 Ralph LeVan recently added OpenSearch capability to the Virtual International Authority File (VIAF). Since the VIAF site is built on top of SRU, the easiest way to that was to use proposed SRU extensions. Here is Ralph's description of it:
VIAF is a joint project of the Library of Congress (LC), the Deutsche Nationalbibliothek (DNB), the Bibliothèque nationale de France (BnF), and OCLC. The project's goal is to lower the cost and increase the utility of library authority files by matching and linking the authority files of national libraries.