There’s also StoryGraph - it’s not federated, but ran by a tiny UK company, but seems pretty popular. I like the content warnings feature and stuff like readers rating the pacing and moods of the books, which is then displayed with graphs on the book page, but they have also introduced some AI features :/ (fortunately opt-in)

check out this comment

PieFed has its own share of dodgy stuff:

• opinions of the dev are hard-coded into PieFed’s code with overreaching content blocks, and error messages deliberately lying to users
• plus a 0/5 priority of testability, 1/5 priority of reliability and 2/5 priority of security described in their architecture document

instead of Piefed :)