It's a multi-fandom, small/rare fandom fic exchange that's grown and grown. There's book, anime, movie, tv, rpf, historical and everything else in between fandoms. This year according to stats there are 2911 fandoms represented with 12205 characters listed.

One of my all-time favourite fics, Killing Elvis (http://archiveofourown.org/works/37677) was a product of Yuletide.