If you are working on a ruby application that requires dealing with credit cards, you are probably using ActiveMerchant. If not, you probably didn’t know about ActiveMerchant.

ActiveMerchant is an extraction from Shopify. It’s a simple to use library which translates one common interface into the wire language of 30-40 different payment processors around the globe with more added at rapid pace. As long as your application can talk to active merchant you can switch payment providers with a single line of code.

Treat yourself to Cody Fauser’s excellent ActiveMerchant PeepCode PDF which is an in depth discussion about the library and covers topics such as order pipelines, order state management and the appropiate unit testing which a financial application requires.

Cody is the main programmer ActiveMerchant which I originally started. Cody took the library further than anything I envisioned and it’s now one of the most competent libraries for ruby.