A rather simple example of implementing a customer billing system.

The Database
The Database API
Perl module implementing simple database interaction operations.
User Management Scripts
A couple of command-line scripts to add, display, and delete users.
User Management GUI
A CGI script to add, display, and delete users.
RADIUS Accounting File Parser
A Perl module to parse RADIUS accounting files.
Billing Script
A script to send email bills to users.