Android has a unique advantage, over most other operating systems, in that it’s display server permits an app to have a transparent background.
On the Android SDK side, it’s quite simple to do (instructions here: How do I create a transparent Activity on Android? - Stack Overflow )
I wonder what it would take, from the Unreal Engine side of things, to get a completely transparent app in UE4 (whilst allowing components in the scene to still be rendered)
A bit of background behind my interest of this: I’m trying to build an app where you would have a virtual character overlaid over the rest of the OS.
I would imagine it would involve playing with the OpenGL canvas and setting the transparency of this accordingly.
Any help or pointers to resources will be greatly appreciated and up-voted 
Thanks,
James