gr-stacks in the literature

Dear all, after a bit of searching, I cannot find much in the literature about gr- stacks, more specifically, charts and presentations thereof reflecting (in a non-technical sense) the group-like structure. Also, aside from self equivalences of gerbes and quotients of groups (G/H for non-normal H), I cannot dream up other "interesting" examples - and these are the opposite ends of the spectrum I want to consider. All pointers welcome. -- David Roberts Pure Mathematics University of Adelaide South Australia, 5005