An ecommerce application that simplifies the card acceptance and authorization process for bricks-and-mortar businesses as well as online retailers. This equivalent to a physical POS terminal handles the transaction between a merchant and the processor. UniPay is one example of a payment gateway.
UniPay Gateway: Open Source Payment Gateway
How to Choose the Best Payment Solution
How to Own a Payment Gateway
What is a Payment Gateway
What is Recurring Billing?
How Payments Work
What Should an Ideal Payment Platform for Investors Look Like?