We're interested in exploring cryptographic anonymization. But the truth is, most groups don't need it.
What about using SMS/Facebook auth?
for auth at the moment we have (in no particular order):
google, facebook, persona
groups can set their own threshold for entry. one option is manual approval where the applicants email is visible to coordinators and the applicant supplies an introduction.
simple but quite effective
it doesn't. The use-case is high trust groups not mass voting.