If you are running a cutting edge version of Google Chrome, Canary for example, you may have noticed the new "You" menu at the top right of the browser.
As it stands, it will eventually be moved to other versions of the browser including beta and stable versions.
So what is it for? It is a menu for Google Chrome's profile manager. It enables you to create multiple profiles, for instance for different users who share the same computer or activity-based, and also to run Chrome using a guest profile.