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+.
Yahoo! has announced the rollout of some limited tests for OpenID's Simple Registration specification. If you're not familiar with OpenID, it's an innovative way for handling user authentication that provides a free and easy way to use a single digital identity across the Internet.
Nexmo offers a series of cloud-based communication APIs that make it easy to integrate reliable communication services into any application. This tutorial by Tim Lytle on the Nexmo blog shows followers how to build a simple text message group chat using the Nexmo SMS API and PHP.