Userrole Manager

Hey,
We need a plugin that add advanced user managment.
For example: Usergroup(role) “adminofa” can list and edit users with role “a”
Usergroup(role) “adminofb” can list and edit users with role “b”
Usergroup(role) headadminofsomegroups can list and edit user with role “xxx” and “xy”
but he can’t see the userlist with roles “b”
and so on…

I think thats some big changes on the user.php site, buty maybe you can help me
Thank you!
reggards