Here is
a website with lists of organizations with open access publications. They are not all schools. I don't know how exhaustive or complete the lists are, but I think that they are close to it.
There are so many organizations now with open access content that they are organized by continent, then individual country. Also, you can do searches for items on particular subjects, across all of the organizations. Links near the top of the webpage whose link that I gave you above will get you to both of those.
There is another site, actually, a couple of them, which lists organizations with open access content. But when I did a search of my browser's bookmarks a few minutes ago, I didn't see them. I will look again later or, more likely, I'll run across them before then while looking for something else.
ADDENDUM: BTW-"open access" is not necessarily
free. Some organizations will offer "open access" content, but charge for it. There was one site that I was at a day or two ago that had two tiers of what they called "open access." One tier had completely free books and the other one they labelled "freemium." Well, there was nothing "free" about that content, although they may have been (I don't remember noticing) selling the books at less than their value was or what comparable ebooks would sell for.