The official Stormpath Ruby SDK by Stormpath calls the Stormpath REST API which provides developers with a user management infrastructure. Features include authentication, schema-less user data and social media login with Facebook and Google OAuth. It requires Ruby 1.9.3+.
There is a category of vendors on the rise in the API space; Integration Platform as a Service (iPaaS). The term is fairly new and there is some debate as to the definition and features of vendors that would be classified in the iPaaS category. This post is an overview of iPaaS and features several vendors that offer iPaaS solutions.