The project is not only a wiki, but also includes a chat server (XMPP/Jabber), a forum, email, file storage, and more. With your membership credentials you can use all services. Essentially, the FeministWiki project offers a "digital home" for the global (radical) feminist community.
Contact me here, or at twitter.com/@socjuswiz (quickest option), or at admin (at) feministwiki.org to get your membership.
Members are added manually by existing members to prevent abuse, but if you tell me you're from the Sinfest forum then I won't scrutinize you much, maybe just write a sentence or two about what feminism means to you.

Full disclosure: Like Tat, I'm a male radfem supporter. In context of the FeministWiki project, I'm the "technician" but not any kind of community leader, since any feminist community ought to be led by women.