Ruby Framework for Interacting with Amazon Alexa is called Ralyxa. Ralyxa is used for creating web services that provide Alexa skills.
This is an exceptional case because of Sinatra framework, Ralyxa designed to work with. As you know, Syndicode prefers Ruby on Rails. But we do not limit the number of technologies and tools we work with.
However, Ralyxa can be used with a few other web frameworks.
An example application implementing the gem can be played with here.
Find more about Ralyxa on GitHub.
p.s. check the latest Sinatra v2.0.1!