I\'m looking for generic and open source payment libraries that support many different payment processor APIs. In other words, I\'d like to develop an application using a single
omnipay is the best solution for PHP
There is django-bursar for use with django.
There's a python port of ActiveMerchant called OpenMerch, which looks quite similar to the ActiveMerchant code.
You can checkout J2pay its clean and its supported gateway list is continuously increasing.
I originally left Node.JS out of the list of server-side technologies, but I'm starting a project that is going to use it. And I found what looks like a great payment gateway library for it. Paynode is similar to Ruby's ActiveMerchant, but in Javascript running in Node.JS. It supports Payflow Pro, Authorize.Net, Braintree, Chargify, etc.
What I have seen done is just wrapping Active Merchant into a light weight web service which exposes a rest API that any of your languages can talk to. This was for a larger company that could properly lock down their networks though, so DYODD.