Access control

The userplus module enhances Drupal's user administration and Organic Groups' subscription administration by allowing administrators to add multiple users at once, make multiple group assignments at once, and make multiple user role assignments at once.

Enables "Shared Sign-Ons" between related Drupal sites on one server with a shared database. Can be used standalone, but is most tested in conjunction with the domain (aka Domain Access) module.

Allows site administrators (or anyone with enough permissions) to switch users and surf the site as that user

The Path Access module gives site administrators an additional layer of access control to all pages of a Drupal site.

This module provides advanced email address checking.

The Bio module allows each user to create one (and only one) "bio" node. Any node-type can be assigned as the bio or Bio module can provide its own node type.