http://circlinghandbook.com/ gives an overview.
It's popular with the Bay rationalists and we have now a biweekly Circling for rationalist event in Berlin. My first contact with Circling wasn't with the rationalist crowd but with other friends in Berlin. I have also other facebook friends from another personal development context that do Circling in the US.
Followed your link; what is it they do? Something like friendly discussion?
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