@maria PT is the only other one I use myself right now. Some other worthy ones, which I do not personally use but do look promising are https://pixelfed.social (federated Instagram alternative), https://write.as, (federated Medium/blogging), https://joinplu.me, (also federated blogging) & https://funkwhale.audio, (federated music sharing/streaming).
I am also writing an #ActivityPub server myself, fediQuest, which fills the role of a federated Quora/SO alternative, but no site yet.
Hi there! I am a free software developer. I enjoy working on useful software, as well as advocating for software freedom and the use of open standards, promoting data ownership, decentralization and privacy. If this is important to you, I may be worth following. If you like Go, Rust, or Swift, it may be worth following me as well. Besides computing, I enjoy metal, a good read and occasionally some gaming, (not much time for that these days).