This one is informal, and doesn't have a strong community yet, but it is growing. It is promoted by Adrieal Wallick, here's her GDC talk http://www.gamasutra.com/view/news/227022/Video_Lessons_learned_from_trying_to_make_a_game_a_week.php .
Here are the Guidelines:
- WEEKLY DEADLINE
- SHARE THE GAME, GET FEEDBACK
- TRY TO CHANGE IT UP EACH WEEK
- REFLECT ON WHAT WORKED AND WHAT DID NOT