Open access is free, unrestricted access to high-quality research materials. Information is not found behind paywalls.
Academic institutional repositories have off open access to scholarship often through preprints.
Subject repositories are open to scholars all over the world who publish work in a particular discipline. Some of the larger ones include:
"When you use the Button, it'll either take you straight to a free copy of the research article or help you ask the author to freely share the article with you."