Several websites and databases act as gateways to grey literature:
OpenGrey: A comprehensive database of grey literature in Europe, offering open access to a wide range of documents.
GreyLitReport: The Grey Literature Report database, focusing on literature related to health, science policy, and public health.
GreyNet: An independent organization dedicated to promoting access to grey literature, providing links to various sources.
OpenDOAR: A directory of academic repositories, many of which contain grey literature.
Google Scholar: This search engine includes citations from both grey literature and academic publishers, making it a valuable tool for researchers.