The “Katta” model  is developed by Prof. Milind Watve at an educational institute in India. A katta in Marathi (the regional Indian language) means a place where people can meet, ask questions, and exchange ideas. A meeting is decided and invites are sent to people who have shown interest. These meetings are held regularly (usually once a week). The important thing is that the meeting has no agenda. There is no upper limit to the number of participants but, I think, the usual attendance is about 50. Although most of the attendees are graduate or undergraduate students, there is no age bar. The sessions usually start by picking up from the earlier session. Participants add their views and the discussion continues. Since the discussion has no boundary, the topic of discussion spans across multiple fields. This provides newer dimensions to look at a particular topic.
Participants ask questions pertaining to the topic at hand. Many questions arise and quickly subside. However, some questions seem to interest more participants. This often ignites a participant, or a group of participants, to investigate the question more deeply. They spend some time doing their research and then present what they discovered at a later katta (meeting). Sometimes the question is investigated in a scientific manner (taken up as an official project by the participants), using laboratory tools, statistics, or field studies, as seen appropriate. These investigations have also been successfully completed and published in science journals.
Prof. Watve's role in all this is that of a catalyst, providing a safe environment where the participants can ask a question without worrying about whether it is good, bad, intelligent, or crazy. Usually, none of the participants is an expert on the topic of discussion. The participants are encouraged to pursue the question and think in ways that possibly may not have occurred to scientists in the field. The participants have the freedom to choose a question of interest, have an opportunity to research the answer, and then have an opportunity to teach others (peers and the moderator) what they learned. 
The topics have the widest range possible and they are discussed with the intention of understanding the underlying science. The Katta model started as a way of getting students interested in science and teaching them the research methodology. It grew to the point of completing several research projects and publishing peer-reviewed articles. Such meetups can be replicated or even expanded to accommodate a large number of experts from different fields.
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