Hello Earl_D (@earl_d),
Thank you for writing to us. Communities extension will allow users to be part of multiple groups. There will also be options for open and closed groups, membership requests and an approval system. As part of broader expansion of ProfileGrid capabilities, this will complement extensions that enhance Group Leader privileges (with frontend group management area) and add option to have multiple group admins.
All of this is currently under development and will be delivered as combination of extensions and enhancements to the core.
Let me know if you have any other questions.