These scripts can be used to audit which roles and privileges a user has, which users and roles can access an object, which users and roles have a particular role and also the users and roles that have a particular system privilege. check_parameter.sql can also list the details of any initialisation parameter.
All scripts can print the results to a file or to the screen. Also each report is hierarchical, so that roles granted to roles etc are displayed.
These scripts have been very popular in terms of download, so if you are using them and find them useful you may want to get the updated versions.