Have I got a deal for you - or rather, these folks do:
Free eBooks | Project Gutenberg (https://www.gutenberg.org/)
Take a few minutes to stop by and browse.
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This is a very esoteric mix of titles, from pulp fiction, SciFi (yeah!!) to out of print books on history.
For example, I pulled multiple period books covering the Boar Wars for background research on my book,
The Prism Mysteries : The Story of the Mummified Stranger (https://www.amazon.com/Prism-Mysteries-Story-Mummified-Stranger-ebook/dp/B00VKZH3KO?ref_=ast_author_dp&dib=eyJ2IjoiMSJ9.qwprRreMwm03HiXyhfrLDz0gyQTpJ3VLeMP7B2NfEIY9TxUASCLUfI08v-rWWyWMdyZarlnGnn31KAIQT2YGsyvScJsCykYjXQxdVUTkXW_BbaY9JWbNnKsZ5Wk52plDWlHej3L_lMQ8g1sUPCE2MUoIAZ7jj-_2makh8Mrh1F4m0G4uSsi0wnJACDWJXPDpxFAmbjHG0CF_6mzpN-log3IsLm0kFDv8S_T2_aea0sA.FMo4yAaP7vyVASWZgIfgF6zHIzvSLRky6RgzuBBFunA&dib_tag=AUTHOR)