However, the apology [0] says that the creator did not "intend" to participate in AI that can "create zero-effort impersonations of artists." I'm not sure if the wording is unintentionally vague, or if there is some way his project could be used in that way.
For what it's worth, the Computational Story Lab's hendometer [1] seems to have largely out-of-copyright books from Project Gutenberg, plus the Harry Potter series.
[0]: https://blog.shaxpir.com/taking-down-prosecraft-io-37e189797...
[1]: https://hedonometer.org/books/v3/863/
Edit: Apparently he was working on an LLM project. https://twitter.com/stealcase/status/1688721685585809408. It's unclear whether he was planning to use the books he scraped (although as @stealcase points out, GPT-Neox itself was trained on books that were pirated).