It looks like you're using Internet Explorer 11 or older. This website works best with modern browsers such as the latest versions of Chrome, Firefox, Safari, and Edge. If you continue with this browser, you may see unexpected results.
American Council of Learned Societies - "a digital collection of about 5,000 full-text titles offered by the ACLS in collaboration with twenty learned societies, nearly 100 contributing publishers, and librarians at the University of Michigan’s Scholarly Publishing Office."
Unlimited simultaneous users.