SectionSixx is an old, very private writer's group. We're accepting new members, although we do ask you to use the contact form (linked here) to request access. The site focuses on encouraging critiques and has birthed a number of successful authors.

You are welcome to post short stories, poetry, and even novels (although be aware that novels may take longer to get a response). The site uses WordPress with bbPress as the forum at this point.

If you're looking for an intimate location to share your work privately, this may be a great fit!