Well, I just wanted to write one which I was confused about when I can here. Though all the rest are already here...
Drabble: Short story around 100-600 words, though the word count varies.
I remembered another one, but i think it's only for the Gryffie tower. Not sure if the rest of the Houses have it. Anyway-
TWS: Three Word Story. Anyone can go and add three words to the story. You can post as many times as you want as long as there's no double posting. Just a little warning- It is VERY insane in there so be prepared. I know because I'm one of them . This applies to Gryffindor only. As I said, I don't know if the other houses have it.