Floating action button on other app and in launcher

I have been searching for a floating circle button that I can interact with everywhere like luncher or in whatsapp and etc ...

so far I only found the action button witch introduced in lollipop. this question may has been asked before and i didn't know the right terminology to search in google. I have seen other apps uses these kind of button. so please help me out here

how can I place a floating button on screen which appear every where. something like AssistiveTouch menu button in IOS which can be dragged everywhere.

finally i found the solution with this awesome repo. use this library :) ===> Floating button in github

here is how it look like :