100words is a weekly drabble challenge community where you respond to prompts that are posted every Tuesday with exactly 100 words.
beautifulmechanical is a community to share music.
ficreadersadvisory is a community where you will be able to talk about and share thoughts on various fanfic.
12monthsofmurder is a challenge where you choose a character and let them die each month of the year.
worldbuilding_exchange has
accepting nominations until January 15th, 8PM MST.
idproquo, a fic/art multi fandom freeform exchange for "iddy" works, is
open for sign-ups until January 17th, 11:59PM EST. The rules and schedule can be found
here.