Available without an NYPL Library card:
The HathiTrust Digital Library is a collection of digitized books from libraries around the world, many of which are in the public domain and can be read at no cost online. Note: you may need to be onsite at any NYPL location to download select items.
The Internet Archive provides access to millions of titles. For some titles, users must sign up for a free Internet Archive library card.
Digital Research Books (Beta)
NYPL has developed Digital Research Books, an early beta test of a new project that collects digital versions of research books from many different sources — including Open Access publications — into one convenient place to search.
Use at home with a Library card and pin: