Taking old books (by others) and publising them on Kindle.
Because these works are so old, they’re available online for free – but many Amazon shoppers and Kindle owners will pay to have them delivered straight to their device.
Public domain books are free to
Once they enter the Public Domain, there is no copyright infringements. You can re-format and even translate the book and sell anywhere.
You can even create and sell the paperback or audiobook version of a public domain book.