Groups can be public or private.
The admistrator has the option of who can be part of the group as well as if they have the ability to post or just read messages in the group.
Messages are organized into threads.
Threads can be assigned categories. This allows your group members to select the categories they want and threads in those categories will be presented to them first.
Members have the option of receiving messages by email. They are also able to reply directly to those messages instead of having to use the web site.
If receiving every message becomes too much, members have the option of receiving a daily summary in their email each day with all the messages (or in their selected categories) posted to the group during the previous day.
A poll can be attached when creating a new thread. Polls can be single or multiple selection.
Track how many message are going through your group each month. See which users are posting the most messages (all time or monthly). Also, see the threads with the most messages all time.
The group administrator can close responses on threads and decide to make a thread public (even in a private group), which will allow anyone to see it.