The IBM Watson Ruby SDK by suchowan is a gem that allows developers to integrate the IBM Watson APIs into their Ruby applications. Usage examples are included in the documentation.
The stakes for Machine Learning APIs are increasing by the day. Major vendors are making moves towards releasing ML platform APIs. One such release is the Cloud Natural Language API, an API from Google that provides devs the ability to investigate the structure and meaning of text via REST APIs.
San Francisco startup Prior Knowledge recently released in public beta their predictive analytics API called Veritable. They want to enable every developer with big data prediction tools, without becoming a quant genius first. Just upload a dataset, execute analysis, make predictions and watch the sparks fly.