So far, I've seen communities that allow people to post original fiction, fan fiction, daily prompts, memes, etc. but I have yet to see a community where original/fan fiction writers can go to get constructive criticism and improve their writing. Of course, there's the How's My Driving? Concrit Meme, but that's more for role players and focuses on how well a character is portrayed than the story. I think such a community where writers could to get critiqued would be useful.