PayPal Payments Pro/Adaptive Payments PHP Class Library includes methods to easily integrate all of PayPal's APIs, including PayPal Payments Pro and Adaptive Payments. It makes it extremely quick and easy to tie PayPal into your applications. It comes with template solution files for nearly every API call available. All you have to do is populate the request parameters, and you'll get a PHP array result which includes everything you'll need from the API call.
CodeIgniter for PayPal Payments Pro includes every API call available in PayPal's NVP documentation, as well as their Authentication and Permissions APIs. The controller includes "template" methods for every call which include all the possible parameters which can be passed into each particular call. All you have to do is fill the blank parameters in the array templates and pass the results into the library method. An array will be returned with all of the response fields from PayPal, as well as a few extra fields for troubleshooting purposes.
FileMaker Custom Functions for PayPal APIs provides a collection of custom functions for FileMaker Pro which provide direct access to PayPal's Web service APIs using nothing more than simple functions inside FileMaker calculations, just like any other FileMaker function. When the solution file starts, it loads a number of functions into your FileMaker system; you'll find them under External Functions from any calculation dialog. There are matching functions for each API call which PayPal provides in their NVP Web services. You simply choose a function and populate its parameters using your FileMaker data. The function will handle all communication with PayPal and return all response data back to the solution file in global fields so they're available for you to populate your own FileMaker tables/layouts accordingly.