NEW MAINTAINER WANTED! Contact me if you want to maintain this module.
This module allows you to, for each group type, specify a list of roles that group administrators are allowed to assign. However this assigned roles are sitewide.
For example, if you created a "trusted user" role, and a new node type called "official group," you could allow administrators of only official groups to add selected other group members of to the "trusted user" role.
This module is currently abandoned. Check project OG User Roles which offers more functionality and it allows setting different roles per group for one user, which makes more sense for majority of usecases.