The Paypal Assistant allows you to use conditionals that must pass to allow actions to be completed. For example, you can create a conditional that if the order status is "Pending" send an email to the buyer that the purchase in on hold until the E-Check clears.
You can also do conditional on the data Paypal includes in it's notification. For example, if the buyer is from the UK, you can send the buyer an email you want sent only to a a UK customer.
Ship your digital goods to your customers automatically by creating a send mail action!
The possibilities are ENDLESS.
All transaction data is stored and searchable.
There is even a Wildcard action that you can define that will be performed if you receive a payment for an unknown item.
The Paypal Assistant can also utilize the Paypal Developer Network Sandbox accounts if you want to test your actions before you go live!
The package comes with BOTH versions which you can use separate or together. The only difference between the PHP and CGI version is the code they were written in, and that each can only execute code on actions in their native language (PHP for the PHP version, Perl for the CGI version).