I guess you have seen the new Android design guidelines, with the new \"Floating Action Button\" a.k.a \"FAB\"
For instance this pink button:
You can import the sample project of Google in Android Studio by clicking File > Import Sample...

This Sample contains a FloatingActionButton View which inherits from FrameLayout.
Edit With the new Support Design Library you can implement it like in this example: https://github.com/chrisbanes/cheesesquare