Amazon FPS vs Killbill: What are the differences?

Developers describe Amazon FPS as "Charge Amazon’s tens of millions of customers using their Amazon account". With Amazon Flexible Payments Service developers can accept payments on their website for selling goods or services, raise donations, execute recurring payments, and send payments. Amazon customers can pay using the same login credentials, shipping address and payment information they already have on file with Amazon. Amazon FPS supports the processing of payments using credit cards, bank accounts and Amazon Payments account balances to send or receive money. On the other hand, Killbill is detailed as "Open-Source Subscription Billing and Payment Platform". Kill Bill is a platform for subscription billing and payments integration Its plug-in architecture allows you to easily apply custom logic and integrate with third party systems..

Amazon FPS and Killbill can be primarily classified as "Payment Services" tools.

Some of the features offered by Amazon FPS are:

• Accept one time payments on your website for selling physical goods, digital content, and services
• Execute periodic or delayed payment features required by subscription and usage-based services such as digital music and online storage
• Facilitate transactions between a buyer and a third party seller, take a cut of the transaction, and have control over who pays the transaction processing fees

On the other hand, Killbill provides the following key features:

• Invoicing and Prorated Billing
• Event Based Billing
• Internationalization

Killbill is an open source tool with 1.93K GitHub stars and 450 GitHub forks. Here's a link to Killbill's open source repository on GitHub.