user groups

Is there a plugin to add “user groups” functionality to WordPress?

I’m asking about something different to Roles. With roles you assign what power a user can access wordpress and users are only assigned one role.

What I would like to do is be able to create user groups where it does not affect Roles and that users can be part of multiple groups.

I guess it can be done using the Roles and permission system where a user in a particular group is given a capability to access a specific group…