An archive that I've belonged to for some years has recently started something new: Fic Trade. Users can sign up and submit prompts for stories that they really want to see written, but can't do it themselves or want to see what someone else will do with it. It's like Secret Santa. Each participant gets assigned an author and they choose one of their prompts to write. All the non-chosen prompts go to authors that sign up as spares.
I did the first round, and I met a LOT of great authors and made some connections I wouldn't have made otherwise. I thought it'd be a good PR plus writing practice opportunity. ^_^
Here's the Round 2 Registration Forum, you'll find all the rules and info here.