I work in Groove all day long, and so here are some ideas taken from that experience:
1) the ability to organize workspaces, to which one could then add tools such as a calendar, case management, discussion threads, files, web url's, etc. With others invited or not, having roles that are workspace defined and then give different permissions for the tools.
2) of course, the addition of the tools described above.
3) integration of email with workspaces based on rules, so that "email" is also a tool of a workspace, and email is copied/moved to one or more workspaces based on rules or manual action.
4) the tools should be extensible in terms of data structure and design, so they can be modified to fit.
You might have all of this planned already: is there a roadmap?