The Standard Ebooks project is a volunteer driven, not-for-profit effort to produce a collection of high quality, carefully formatted, accessible, open source, and free public domain ebooks that meet or exceed the quality of commercially produced ebooks. The text and cover art in our ebooks is already believed to be in the public domain, and Standard Ebook dedicates its own work to the public domain, thus releasing whole ebooks files themselves into the public domain.
via https://standardebooks.org/about/