Baker's Dozen is a game I've seen played on the Internet Movie Database Message boards (
IMDB Message Boards) although I've seen similar games on Gaia, too.
Anyway, the object of the game is to generate lists of 13.
The first person names a topic, and gives the first list item, the second person adds the second item, the third....until the 13th answer. The 13th person adds the last item on the list, chooses a new topic, and puts the first item on the new list.
Next topic:
13 Creatures from the Harry Potter series
1. House Elf