The DPLA is an online collection of over 36 million free digital materials from libraries, archives and museums. Its digital exhibitions and primary sources cover everything from the 1918 influenza pandemic to the golden age of comic books.

The Nautical Archaeology Digital Library, a collaboration of Texas A&M University and ShipLAB, contains searchable shipwreck databases and ancient ship models.

The online collection houses items from FOIA and CIA release programs, including more than 50 years of CIA information on UFOs and a collection dedicated to the oldest classified documents in the US.

The Biodiversity Heritage Library provides open access to biodiversity literature. The archives are home to curated collections with books from Charles Darwin's personal collection to field diaries from explorations of Antarctica.

The New York Public Library's online collection contains nearly 890,000 digitized items. Its archives and manuscripts cover books, prints, photographs and more unique collections, like a massive database of over 17,000 historical restaurant menus.

The History of Medicine Division at the National Library of Medicine contains a vast collection of digital materials related to health and disease. Through its online resources, patrons can view the earliest anatomical drawings, read about the history of forensic medicine and explore an exhibition dedicated to the accomplishments of women physicians.

The Getty Publications Virtual Library hosts an impressive collection of art books, with more than 300 publications that can be read and downloaded for free, including some that are out of print.