title: How to make an Android application to run some UI element above other application?
body: <p>Sorry if the title is it's not self explanatory. </p>
  
  <p>I'm trying to make an application that can interact with other ones by adding them a graphic element in their UI.</p>
  
  <p>Just like Google does with Google Translate new function. 
  You can see a graphic example here: <a href="http://cdn1.tnwcdn.com/wp-content/blogs.dir/1/files/2016/05/TTT_DogfoodGif_v01_JRS.gif" rel="nofollow">EXAMPLE GIVEN</a></p>
  
  <p>My questions are:</p>
  
  <ul>
  <li>Is that even possible? (I guess it is)</li>
  <li>Where can I start searching about this? I haven't seen anything in Androids Developer documentation. I really don't know how to search info about this.</li>
  </ul>
  
  <p>Thank you all.</p>