title: How to implement a popup overlay that can be displayed over any other app in Android
body: <p>How can I implement a popup overlay for an app that can be displayed over any other app. </p>
  
  <p>Facebook implemented a very similar feature called Chatheads in its new Facebook Messanger version. I was really surprised to see that this is some how possible. On the image, you see a chathead (dog on the right) over another app. </p>
  
  <p><img src="https://i.stack.imgur.com/hWk4r.png" alt="Facebook Messanger&#39;s Chathead over other app"></p>