Like what? Rails is great for APIs, because APIs, especially RESTful and Hypermedia APIs, can literally be a standard webapp with JSON views instead of HTML.
I've never built a SOAP API in Ruby, so maybe Rails wouldn't work with that very well. XML-RPC might also be a little tough, but I honestly can't think of any significant difference between a "traditional web app" and a RESTful API. They're a perfect example of code reuse in MVC (or Model2 if you want to be pedantic).
I've never built a SOAP API in Ruby, so maybe Rails wouldn't work with that very well. XML-RPC might also be a little tough, but I honestly can't think of any significant difference between a "traditional web app" and a RESTful API. They're a perfect example of code reuse in MVC (or Model2 if you want to be pedantic).