Green Open Access (where authors make an early version of an article available in an online repository) is sometimes promoted as a way of ensuring public access to research, but many funder policies encourage or require Gold Open Access as the preferred route to public access, as this ensures maximum openness and re-usability of research results. Where Gold OA is supported by an article processing charge (APC), some research funders and institutes will cover this cost for their researchers. 

For more information on the OA mandates and policies adopted by governments, research funders, universities and institutions, see:

SHERPA / JULIET : Allows you to search by funder name or country keyword.
ROARMAP : Allows you to search by multiple fields, including by country and type of institution.
Plan S: Our journals offer the Gold OA route to Plan S compliance, but the License to Publish agreements authors sign with our journals are not compatible with the Green OA route to compliance and are not compatible with Plan S's Rights Retention Strategy.

(Note that these resources may not be comprehensive).