Public Domain books sharethread.
Post here your favorite PD books, and share online sources for PD books.
There's no general hard rule, but if it's older than 100 years old it's probably in the public domain, unless it's being held under IP by some institution. If it's on librivox.org or gutenberg.org it's PD. Most Creative Commons stuff is actually PD because if they don't do the copyright paperwork, the CC license is not legally binding.
Some optional prompts:
> What are five PD books you think should be in every home?
> What five PD books would you take to a desert island for ten years?
> What five PD books would you take to a cyberpunk dystopia?
> What are the five PD books you personally liked the most?
> If you could measure how much of a "classic" each book is, what would be the top 5?
> If you could have the superpower of touching people in the forehead and making them know five PD books, as if they had read them (Matrix style, as in "I know Kung Fu"), what five books would you choose?
> If you could snap your fingers and have five PD books of your choosing materialize in front of you, which ones would you choose?
That's too many prompts.