Welcome to lightning_fic. Here, the moderator will post a prompt behind an lj cut, and a time frame. Members are to click on the cut, read the prompt, and use the alloted amount of time to create a ficlet (or short piece of fiction). Then, respond to the entry with what you have created!
It's a great way to keep your brain exercising on some creative writing, without it being something you need to worry about extending or polishing - and you can see the variant ways that other people respond to the same prompts you do.