Thanks to the National Genealogical Society (NGS) blog I've learned about Internet Archive, a non-profit digital library aiming to provide "universal access to all knowledge." Internet Archive offers borrowable books in three formats: BookReader, PDF and ePub. You can borrow up to five books at a time. Each loan expires after 14 days and is automatically returned at the end of the time period.

Just for fun I queried Irish genealogy, and up popped nine titles, five immediately available to borrow and four for which you can be waitlisted. Check out (yes, a pun!) Internet Archive books here: https://archive.org/details/inlibrary. And if you'd like to read the NGS blog posting, which also talks about JSTOR for borrowing periodical publications, here's the link:  http://upfront.ngsgenealogy.org/2017/10/did-you-know-that-you-can-borrow-books.html.