Views (6.x-3.x-dev) - not required but its the only way to see the data
These modules are a requirement because they help to keep clean session data. Its highly recommended to limit the sessions to 1 per user.
How it works
When a user logs in, the session count field is incremented for a user and their session id and creation time are saved for later use. When the user is logged out, the session's time span is added to the user's elapsed time.
An abstract implementation of the Drupal Queue API. It will contain multiple strategies for cache managing, and it is possible to easily plug in different backends (like APC or memcached).