These are open access versions of articles sourced through Unpaywall.
What does this mean? Unpaywall is a database of “freely available” versions of articles. Alumni, Community Users or anyone can click on the OpenVersion link when it appears and be taken to a version of the article without authenticating (no CWL or EZproxying needed). FAQs can be found here.
Note if citing the article that the Unpaywall version may differ from the final published version.