Yuletide is an annual obscure fandom ficathon, where participants offer to write a minimum of 1000 words in one of a hefty list of fandoms, and in turn receive a fanfic written by someone else. You choose which fandoms off the list you offer, and which characters in those fandoms you feel comfortable writing, but you must offer at least three different fandoms. Likewise, you must request at least three different fandoms for the system to choose from for the fic you receive, and you can request a fourth. Once you get your assignment, your fic is due by December 19th. Check out yuletide and yuletide_admin for more info.
This is the fifth year for Yuletide, and they're up to 1130 participants. Take a look! It's a fun way to both give and get some fic in fandoms that just don't get enough writerly love. ^_^