A repository is a collection of other smaller OA sites and collections. Repositories are useful for searching for other OA collections.
These are collections of OA journals. You can search by title and content keywords.
Academic institutional repositories have off open access to scholarship often through preprints. Most institutions of higher education have an institutional scholarly repository. You can search by institution name and "OA" or "repository" They are often housed through the institution's library. Here are a few examples:
Authors often retain the right to their scholarship and make them available on scholarly sites.
Subject repositories are open to scholars all over the world who publish work in a particular discipline. Some of the larger ones include:
OA theses and dissertations through Ebsco