Wikipedia or other Wikimedia projects simultaneously. It provides an opportunity for real-time and location brainstorming and collaboration.
Coming together at the same time and at the same place does not cut it. So the first Indian WikiMarathon is happening at the same time, in multiple locations and on the Internet. In Chennai and Bangalore people come together while many Tamils are getting together without a central location.
This WikiMarathon builds on previous get togethers and will hopefully grow to capture other locations and communities.