You can sign into sites and apps with Facebook and Twitter, and soon you can do the same with your Google+ account.
Google+ sign-in works for Android and iOS apps, as well as web sites. Or at least it will. Right now, Google is just pitching it as a feature that's coming to for developers. So you're not going to see it many places just yet. It's starting with 10 services — Flixster, the Guardian, Fitbit, and others. Google says its login is supposed to be more secure and better at preventing spam.
The rollout is gradual, but so far we've only seen the option to use your G+ account on the Guardian. Unfortunately Google has some catching up to do here. Facebook login is pretty much ubiquitous on the web, and the same network is closely integrated into iOS, as well as a number of Android phones. I dunno, I don't think we all necessarily wanted yet another way to sign into websites, but less Facebook is probably a good thing. [Google Blog]