Annually on the last January weekend, Drupalistas from all over the world gather in local sub-events or join vitual meetings and work together.
Elsewhere such events are known as "Code sprints". But it is not only about code contributions. Volunteers with all kinds of skills are very welcome. They contribute graphics, tutorials, marketing ideas, tests, translations. Or, if nothing else, provide food and keep the attendees happy.
Is your user group organizing an on-site event or virtual co-working space? Add your event as a sub date to the annual series entry!