Gonna get all Inception on you. Watch out.
Say you're surfing a site and think: "Hmm, I wonder if there's an app for that?" (For the site, that is.) Well, the Googlers want to help make your life a whole lot easier by showing you —in your address bar— if there's an app for that.
So to be clear: if you want to know if there's an app for that, there's an app for that. Your brain hurting yet?
It's even really well executed: you add the plugin to Chrome and surf away. If you are on a site for which there is a Chrome app, a small "+" appears in your address bar. If you already have the Chrome app for the site, a checkmark appears in your address bar. No indicator, no app.
Simple, effective. And super meta. What more can you ask for?
Download: There's An App For That Chrome Extension