It may seem like "pretty simple functionality", but...
Active Merchant "raison d'être" was Shopify's requirements for a simple and unified API to access dozens of different payment gateways with very different internal APIs. Abstracting the APIs for dealing with credit cards and payment processors was core to Shopify's business, and they open-sourced what could have easily been kept closed. This abstraction is hard work, not the kind of work I want to do, and I'd rather use their robust library than roll my own or use another poorly-tested one.
We package and deploy Active Merchant in a single, stand-alone .jar file. We don't use Rails (Active Merchant works excellently as a stand-alone library). It's not as complicated as you think.
Active Merchant "raison d'être" was Shopify's requirements for a simple and unified API to access dozens of different payment gateways with very different internal APIs. Abstracting the APIs for dealing with credit cards and payment processors was core to Shopify's business, and they open-sourced what could have easily been kept closed. This abstraction is hard work, not the kind of work I want to do, and I'd rather use their robust library than roll my own or use another poorly-tested one.
We package and deploy Active Merchant in a single, stand-alone .jar file. We don't use Rails (Active Merchant works excellently as a stand-alone library). It's not as complicated as you think.