ppIPN is a CFC used to handle the asynchronous "ping" that PayPal provides (when enabled in one's PayPal account settings) that provides real-time payment transaction data. ppIPN performs the necessary PayPal post-back to validate the initial ping and then iterates through several more validation steps in order to a) ensure the integrity of the call and data and b) capture and persist relevant transaction information.
Because Instant Payment Notification is an asynchronous process, ppIPN's sole means of communicating status, errors, and issues is via email messages.
Security-sensitive settings have been factored out to a supporting cfc called ppSettings, which is included in the download.
Full documentation, explanation, and examples can be found at http://bit.ly/ppIPN

Adobe Coldfusion 7 and above. (untested on Railo or OpenBD)