Twitter Communities is a relatively new feature, it has been out a few months and it’s doing pretty well.
Described “Twitter Communities were created to give people a dedicated place to connect, share, and get closer to the discussions they care about most.
Communities are started and managed by people on Twitter — admins and moderators who enforce Community rules and keep conversations informative, relevant, and fun. People who accept invites to join a Community become members.”
I’d like to see it added to the long list of embedable links if possible. Either the timeline of communities or the join my community option