Janrain Engage and Gigya are two leading providers of “social sign-on” services. If you want users to use Facebook, Google, Twitter (or OpenID, etc) to log into your website for a “personalized experience”, it can be a pain in the a** to code that up. Since you need to keep up with the API of each service, and map the service-specific id to some centralized one that you can keep in a database.
I find that trust is still a big problem in this process. Users seem to be reluctant to log in into any of the website I create using their Facebook. It probably has to do with the general reluctance of a user to click the “Yes” or “Okay” button when presented with a popup. I think a standardized interface such as the one that Janrain Engage and Gigya provide is a step into the right direction, where people will begin to associate this login process with something they can trust.
What’s the difference between Janrain and Gigya? Not much.
Basically, it boils down to Janrain being a little simpler to use but less feature rich, and Gigya having more features and steeper learning curve.