oAuth
Built on top of an Open Source Library
HybridAuth Library enable developers to easily build social applications to engage websites vistors and customers on a social level by implementing social signin, social sharing, users profiles, friends list, activities stream, status updates and more.
23 supported social netwroks
Depending on the audience you're targeting, you can choose from a wide variety of providers and services including: Social networks, Microblogging platforms, Professional networks, Media, Photo sharing, Programmers and Gamers networks.