Google announced the launch of Google+ sign-in, an addition to the Google+ platform, which will enable users of various sites and apps new ways to share with Google+.

Launch partners include: Banjo, BeautyFish, Fancy, Fibit, Flixster, The Guardian, OpenTable, Shazam, TuneIn and USA Today.

“Whether you’re building an app for Android, iOS or the web, users can now sign in to your app with Google, and bring along their Google+ info for an upgraded experience,” says Google+ Director of Product Management, Seth Sternberg. “It’s simple, it’s secure, and it prohibits social spam. And we’re just getting started.”

“If you sign in to Gmail, YouTube or any other Google service, you can now use your existing credentials to sign in to apps outside of Google,” he adds. “Just review the Google+ permissions screen (outlining the data you’re sharing with the app, and the people who can see your activity), and you’re all set. Google+ Sign-In also comes with the protections and safeguards you’ve come to expect from your Google account (like 2-step verification), so you can always sign in with confidence.”

Users can manage signed-in apps, not unlike they can with Facebook, at plus.google.com/apps or open the new Google Settings app on Android.

The launch also comes with the ability for developers to let users install mobile apps for their sites with one click, when the users visit said sites.

Google also plays up the Circles sharing functionality, taking a jab at Facebook-like sharing, calling it spammy.

“With Google+ Sign-In and circles you decide who to share with, if at all,” says Sternberg. “In addition: Google+ doesn’t let apps spray ‘frictionless’ updates all over the stream, so app activity will only appear when it’s relevant (like when you’re actually looking for it).”

“Frictionless sharing,” of course, is a phrase coined by Facebook, in relation to its Open Graph.

Google+ sign-in comes with a new “interactive” post in the Google+ stream, which lets other Google+ users go right to the app where they can buy, listen, review, etc.

Developer documentation is here.