Alex MacCaw commented that "Rails is just an API":
For legacy apps, this is true. My company started using Rails back in 2007 and it was enlightening because it introduced seemingly forgotten concepts in web development like MVC, REST, and included some really nice helpers that made it easy to render stuff client-side. It was a breath of fresh air.
What Rails does have is an awesome tool-chain that includes Sprockets, HAML, SaSS, CoffeeScript, and some really handy helpers. The good news is that these tool-chains are trivially easy to integrate (if its not already integrated) into other fantastic Ruby frameworks like Renee, Sinatra, and Middleman.
Its not too far fetched to think that down the road we'll get rid of Rails for the API server and go with something faster and more "slim".