kenetix writes:  

I've created a PHP license generator script. Basically a script that allows you to generate serial numbers which are bound to domain names with a user-specified expiry date. This is useful if you want to sell or release scripts with serial numbers.

This script is free, and works for any PHP script, including PHP-Nuke. You can get it from Kenetix.net. To view a demo of this tool, visit this link. You can find a collection of other website tools at this page.

Enjoy :)