OpenID, OAuth, Facebook connect, OpenSocial , OpenGraph, "Войти ВКонтакте", XAuth
TweetDeck (for #ipad) - link
TweetDeck is your personal browser for staying in touch with what’s happening now, connecting you with your contacts across Twitter, Facebook, MySpace, LinkedIn and more.
Using XAuth to simplify the social web. - link
In practice, the list of services provided at any given time by xauth.org should not be considered exhaustive, but instead a suggestion for how to prioritize complex service selection dialogs and interfaces, like those known as "NASCAR" interfaces.
XAuth - XAuth is built on purely front end technology taking advantage of capabilities available only in HTML5 browsers. - link
Demo page : http://www.meebo.com/xauth/
Facebook May Launch Recommendation Service For Other Websites - link