masagrator, who’s released numerous 60FPS mods for commercial games, has released Status Monitor Overlay. This overlay homebrew, which makes use of the recently released Tesla environment, lets you see some statistics about the functioning of your system including:

  • CPU usage
  • CPU, GPU & RAM frequency
  • RAM usage categorised into Total, Application, Applet, System and System Unsafe
  • SoC, PCB & Skin temperatures
  • Fan Rotation Speed

Status Monitor Overlay updates on-screen information every second and you may exit it by holding the left and right stick simultaneously. In the future, masagrator plans to add statistics about GPU usage and the ability to reduce window size.
You may read more about it and download it from its GBATemp Thread.