Pillowfort is a new social media / blogging platform. They're trying to be like ao3, but as a catchall for fandom rather than just a fic archive. It's kind of like LiveJournal and Tumblr had a baby. It's still very very new and in beta. You can sign up and pay $5 for an invite key, though sometimes they have a waiting list for free keys. They've been entirely funded so far through a Kickstarter and registration keys. It's really in its infancy still, but so far I like what I see even though it's quieter than Tumblr because they haven't gotten a ton of users yet.