I found a source for non-copyright books. The sight is Authorama listing a number of books in the public domain. On several occasions I have looked for books online to see if there was a particular publication available for free. I never did any good finding what I was looking for. I was actually surprised to find anything in terms of books when I started researching this topic. The site is nowhere near your public library in terms of the titles available however, there are dozens of titles several of which I recognized.
When I was looking at what was available I came across two authored by Mark Twain. One titled Quips and Quotes piqued my interest because I like quotes and anecdotes from wise men of long ago. I have used quotes and expressions on a number of occasions to open classes in the form of icebreakers etc. Other times they can be fun to toss out as a source of humor. The site would also be useful for someone teaching a literature class that required reading one of the books provided. A free book is particularly important in these times of rising tuition costs and class cancellations. This is pretty dry but the truth is that printed books and literature still provide a fundamental basis for all levels of learning.
The books are completely free without restriction. The site asks that if you want to help out provide a link to Authorama and tell other potential users about the site.