Kinmunity - The largest online community serving otherkin, fictionkin, therians, vampires, plural systems, and the other-hearted.
Darkfang Cabal + Chats - A small collective making and running online things for otherkin, nonhumans, alterhumans etc. Forum and chatrooms are 18+
Otherkin Hispano - A Spanish-language forum for otherkin and therians.
The Werelist - A long-standing therianthrope forum which is also welcoming of other kinds of alterhumans.
Draconic - "For dragons, by dragons": A forum and chat for dragon otherkin and other dragon-identified people.