A good user/group role maker

Hello!

Now im tired of looking in the plugins folder.
I need a plugin that gives me the oportunity to make new groups with custom rights.

Like i want a group called “User Admin”. That group should only be able to accept new users that register. Another group is “Cat3 editor” this users is able to edit everything but only in “cat3”.

Is there anything out there that’s not complicated with thousands of extras?

Thanks!