Active Merchant is a Ruby library that allows developers to easily integrate payment processing into their applications. It supports many popular offsite and direct payment gateways. The library was created by the founders of Shopify to handle payments for their e-commerce platform. Active Merchant abstracts away differences between gateways so developers can switch processors easily. It provides a simple API to authorize credit cards, handle refunds and other common payment tasks.

1. Active Merchant Ruby library for dealing with Creditcards, Payment processors and shipping John Ward

4. Offsite Payment Gateways Consumer chooses to purchase on your site Offsite Payment Gateways work by redirecting consumer to another site Form variables are used to identify the product and price Third party site captures the payment. Consumer is redirected back to site along with confirmation of payment.

5. Direct Payment Gateways Consumer chooses to purchase on your site With Direct Payment Gateways you are in control of the payment form. Accept cc details on your site. Call Payment processor web service interface Confirm purchase

7. Offsite Payment Gateway Example - Paypal

12. Direct Payment Gateway Example - Realex