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

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.

Ruby library for integrating with the Braintree Gateway

Stripe webhook integration for Rails applications.

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.

Lightweight wrapper for Paypal's Adaptive Payments API

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

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

Ruby client library for the GMO Payment Platform.

The Square Connect Ruby SDK is retired. Please migrate to the new Square gem: https://github.com/square/square-ruby-sdk

A Ruby gem wrapper for the pin-payments (pinpayments.com) API

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

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

Datatrans Integration for Ruby on Rails

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

Rails javascript plugin for calculating PayPal fees

Ruby library for integrating with the MundiPagg payment web services

Ruby gem for interfacing with Pagseguro V2 API.