This year's
polybigbang (also
here on DW) is open for sign-ups from now until September 20th, which is also the rough draft due date. So, you don't even have to sign up until you're done! Very low-pressure.
The
polybigbang is a ten thousand word big bang challenge that focusses on polyamorous relationships of all sorts. They allow stories from any fandom, or original fiction, plus they always need mixers/artists. Worth checking out!