eBay has integrated Google Sign in to augment their Identity platform.

I work for an ecommerce site and we generally have a diff. sub domain which will have the "beta" or "test" version of code in live. Users are welcome to use it, but with fair warning. We also trickle, small percentage of users to the newer experience to gather feedback before enabling it site wide (A/B testing).

So you're sayign what I can do it duplicate my site onto a subdomain, test the features there, and when they're bug-free, I can just copy paste the new code into the source files on the live site?

Rasberry Pi would be a great gift :)

http://colorpeek.com essentially does the same

Gtihub would be your best bet. code.google.com also support git projects.