Turn Off the Lights is an amazing chrome app, works both on Google Chrome & Chrome OS. This app increases automatic focus on video you are watching and gives you better experience by turning off the screen lights i.e. it darkens all screen areas excluding video thus provides you better video watching experience in just one click. Clicking again returns the page to normal.
Here are some good chrome applications which you can use on chrome and chrome os even without an Internet connection. Using these cool apps you can do some useful tasks like transcribing any audio, access your windows desktop remotely, customize images, manage your emails offline, play your old desktop games like solitaire and more.