A handful more (8, to be exact) open access titles via the same channel(s) are at
www.BibliOpen.org. "BibliOpen.org hosts open access scholarly works from BiblioVault, a division of the Chicago Distribution Center at the University of Chicago Press."
It appears that the 8 titles are in a constant rotation, so that the ones that you see tomorrow, for example, will not be the ones that you will have seen today.