You can enable an additional group option "Forum Priority / Assignment" and get additional features inside Group's forum.
Once you have enabled this option, then while creating a topic, a priority can be assigned by the topic creator.
Group administrators and Topic creator can update the priority later also. Group admin can assign the topics to someone from the group. If a topic is assigned to a user, that user or group admin can re-assign it to someone else.
You will also see these priorities in the topic listing. And you can sort / filter these topics by priority.
Viewing Aggregated list from All Groups
To view aggregated list from all the groups, you can add a custom menu in navigation bar, with url - /oltpublish/site/forum.do?dispatch=listTopics
This url can only be accessed by authenticated users. Topic list provides option to filter assigned topics to all, current or a different user.