Some devices (including several of Samsung's Galaxy phones) have the ability to float videos while you do other things on your Android device. Floating YouTube Popup Video brings that power to everyone.
The app allows you to open up a YouTube video in a small window that you can move across your screen. You can search within the window and use pinch gestures to resize it. Obviously, this works better the larger your screen is, and it's a definite boon for users with tablets or large smartphones.