You can request an invite on the flagship instance and currently they are accepted. Dev’s post: https://friend.camp/@tripofmice/106008396241386134
I’ve been using Bookwyrm for about a month now and it’s really nice to use despite some trickeries here and there. Try it out!
If you never heard about it, it’s a federated reading platform (think Goodreads). You can review, quote and comment on books and interact with Mastodon.