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

In the last few years digital currencies have successfully demonstrated their ability to become an alternative financial instrument in many different markets. Most of the technologies available at the moment are based on the principles of Blockchain architecture, including dominating currencies like Bitcoin and Ethereum. Despite its popularity, Blockchain is not the best possible solution for all scenarios. One such example is for fast micro-payments. Zold is an experimental alternative that enables distributed transactions between anonymous users, making micro-payments financially feasible. It borrows the proof-of-work principle from Bitcoin, and suggests a different architecture for digital wallet maintenance.

Quickly build an online store with carts, orders, automatic email receipts and payment collection via Stripe, StripeConnect, PayPal and Moneris.

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.

Resources and tools for developers to integrate Braintree's global payments platform.

Manage your professional association online. Membership categories, applications to join and reclassify, annual dues payments and more.

Stripe, Paddle, and Braintree payments for Ruby on Rails apps

Mountable rails engine which loads assets (svg files of payment icons) and provides a frozen_record model called PaymentIcon to access these through groups, names of icons, etc.

This engine allows users to inject requests into a queue to be processed. The queue handles bank account validations, credit payments, debit orders and collecting bank statements/notify me statements.

Kill Bill payment plugin for Paypal Express Checkout.

THIS GEM IS STILL IN DEVELOPMENT STAGE. Find documentation here: https://github.com/leandrosardi/invoicing_payments_processing.

M-Pesa SDK for Ruby is an unofficial library aiming to help businesses integrating every M-Pesa operations to their Ruby applications.

Simple REST API for the CyberSource Global Payments Platform

Provides integration with the Fat Zebra internet payment gateway (www.fatzebra.com), including purchase, refund, auth, capture and recurring billing functionality.

[Deprecated] The PayPal REST SDK provides Ruby APIs to create, process and manage payment.

Accepting iDEAL, Bancontact, SOFORT Banking, Creditcard, SEPA Bank transfer, SEPA Direct debit, PayPal, KBC Payment Button, CBC Payment Button, Belfius Direct Net, paysafecard, PODIUM Cadeaukaart and ING Home’Pay online payments without fixed monthly costs or any punishing registration procedures.'

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

Kill Bill payment plugin for Litle & Co.

Offsite Payments is a simple 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 put as simple an abstraction as possible on top of offsite (often called hosted) payment pages, and allow contributors to easily help services such as Shopify extend the number of offsite payment services they support.

Radiant Shop is an attempt at a simple but complete store. It includes Products, Categories, Orders and Credit Card Payments