Manage/Assign Roles to Users Other than Administrators
NOTE: Since Drupal 6 is un-supported now (check announcement), you won't get a module which still have the D6 version actively supported. Also don't expect the module to be supported for any issues.

You can check the Role Delegation module, which allow users to set user roles to other user. Following is the module description from module page:


  This module allows site administrators to grant specific roles the
  authority to assign selected roles to users, without them needing the
  administer permissions permission.


The last release of this module for Drupal 6 version was made available on 9 Dec 2010, you can download it from here.