Active Merchant is a simple payment abstraction library used in and sponsored by Shopify. It is written by Tobias Luetke, Cody Fauser, and contributors. The aim of the project is to feel natural to Ruby users and to abstract as many parts as possible away from the user to offer a consistent interface across all supported gateways.

Stripe is the easiest way to accept payments online. See https://stripe.com for details.

Ruby library for integrating with the Braintree Gateway

Stripe webhook integration for Rails applications.

PayPal Express Checkout API Client for Instance, Recurring and Digital Goods Payment.

Lightweight wrapper for Paypal's Adaptive Payments API

Package to simplify including the Adyen payments services into a Ruby on Rails application. The package provides functionality to create payment forms, handling and storing notifications sent by Adyen and consuming the SOAP services provided by Adyen. Moreover, it contains helper methods, mocks and matchers to simpify writing tests/specs for your code.

Implemention of pain.001.002.03 and pain.008.002.02 (ISO 20022)

Ruby client library for the GMO Payment Platform.

A straight-forward REST API for Amazon's Flexible Payments Services.

A Ruby gem wrapper for the pin-payments (pin.net.au) API

Datatrans Integration for Ruby on Rails

An API for using the Amazon Flexible Payment Service (FPS).

Ruby gem for interfacing with Pagseguro V2 API.

Ruby library for integrating with the MundiPagg payment web services

The PayPal Invoice SDK provides Ruby APIs to create and manage Invoices using the PayPal's Invoicing Service API.

Rails javascript plugin for calculating PayPal fees