PeepSo Groups Addon GPL Overview:

Open, Closed, and Secret user groups. Groups plugin lets your community to create and participate within more narrowed group discussions. Communities, especially those revolving around a general topic, groups are a very useful tool. They allow your users to focus on a particular thing. This plugin also comes with the possibility of creating announcement groups where only group owners can create new posts.

PeepSo Groups Addon GPL Features:

• Create Groups
  Let Your Community create groups for focused discussions.
• Privacy
  Open, Closed, Secret and Announcement groups can be created.
• Group Invitations
  Invite users to groups.
• Add users to the group
  Community Admins can add users to groups.

• Group Notifications
  Groups come with their own set of notifications regarding posts and user actions like invitations.
• Group Categories
  Assign groups to specific categories.
• Optional Announcement Stream Posts
  When a user Posts to stream when joining.
• Pinned Posts
  Pinned posts within groups.

• Admin notifications
  E-mail notifications to Admins when a new group is created.
• Group User Roles
  Group Owner, Manager, Moderator and Member roles.
• Photos and Albums
  With Photos Plugin you can create Photos and Photo Albums in Groups.
• Audio & Video
  With Videos Plugin you can share videos in groups.