Resource Monitor Mini Pro : KF Software House

This is a mini resource monitor. It monitors available memory and CPU loading. It will always stay in the corner of your phone's screen.

Set the overlay to any corners of the screen, customize the color and transparency.

(CPU loading is an estimation for newer device)

Trial version:
https://play.google.com/store/apps/details?id=info.kfsoft.android.MemoryIndicator