Group Join !SIMPLE! v1.1 by ekerner.com
Allow users to assign themselves to groups, and leave groups.
Great for mailing lists, hobby groups, fan clubs, flash mobs, product updaters, and pretty much any kind subscription.
To configure simply ...
Create a new 'Group Join' module, select your desired group from the drop-down list, and optionally set your 'Join' and/or 'Leave' button texts.