Bielefeld Academic Search Engine (BASE) is one of the world's most voluminous search engines especially for academic open access web resources. BASE is operated by Bielefeld University Library.
German Meta search engine, hosted by the non-profit charity organization SUMA-EV in cooperation with the Leibniz University of Hannover.
One of the most important search engines for Open Access Contents. OAIster is a union catalog of millions of records representing open access resources that was built by harvesting from open access collections worldwide using the Open Archives Initiative Protocol for Metadata Harvesting (OAI-PMH). Today, OAIster includes more than 30 million records representing digital resources from more than 1,500 contributors.
BMBF Research Gateway
Search engine of the "Federal Ministry of Education and Research" = "Bundesministerium für Bildung und Forschung (BMBF)". Data from servers of public financed German research organisations, but not all of their institutes.