There are two comms, one for live action (summer_flinging) and one for animanga (summerflinging). The fandom/pairings/rating are up to you. You just sign up for one of the time blocks listed, during which span you're assigned a specific day on which to post a story of 500 words or more, or to post a piece of art. Now, the twist of it is, you sign up under a pseudonym for which you've created a separate LJ. It is, in essence, a fannish masque, and part of the point is experimentation.
Sign ups end on April 18. Posting begins on June 21st and ends on September 21st.