Open Education Resources ("OER"): an umbrella term covering open access textbooks, videos, slides, and other course materials.
While this page contains some information on other types of open access publications and OER, it focuses primarily on open access textbooks.
While these texts are hosted online, they are often available as downloadable files that faculty/students may print on their own. An option common for many platforms is a small (cost-recovery, not revenue-generating) fee to have a text printed and shipped to faculty/students who want to own a print copy.
General info and support on open access and OER
Open Educational Resources at Cornell - an introduction to OER usage, including examples
Open Educational Resources Repositories For Casebooks & Textbooks - an article in AALL Spectrum by Kayla Reed and Karen Shephard
Open access law textbooks
There are many websites hosting, or sometimes merely linking to, open access textbooks. Some repositories contain only texts published via their own proprietary platforms, while others attempt more comprehensive coverage of texts regardless of their original platform. This leads to some overlap in the content available on these platforms.
For more info on publishing your own textbook via one of these open access platforms, please consult their FAQ or other information pages.
CALI's eLangdell Bookstore is a repository of law texts published on CALI's platform and freely available for faculty and students. There is an eLangdell information page for faculty who are interested in publishing law textbooks on that platform.
Professor James Grimmelmann has a website promoting inexpensive and open-access intellectual property and technology casebooks.
While NYU does not have its own open textbook platforms, faculty there have created open access textbooks on copyright law (from Professors Jeanne C. Fromer and Christopher Jon Sprigman) and trademark law (from Professor Barton Beebe). There is a press release from NYU about the effort.