PHP-KeyCodes is a is used to sell software key codes or pin numbers using PayPal or Google Checkout. The key codes are entered into the item details and when a customer makes a purchase, the first key code is removed and sent by email to the customer. This leaves the next key code ready for the next purchase. When the number of codes reach a lower limit, an email is sent to the site administrator. This functionality can be changed because code hooks are available.
The PayPal and Google Checkout ‘buy now’ buttons can be displayed in the admin interface and then copied on to your web pages.
PHP-KeyCodes is based PHP-eSeller and includes many of its features including transaction list, sales reports and email newsletter facility.
For details refer to http://www.withinweb.com/phpkeycodes/