Windows 10 is finally getting a built-in FPS counter
Geforce Overlay - No longer have FPS Counter. Now it's burried under Performance Overlay and has an intrusive border in my games. : r/GeForceExperience
FPS Monitor - Ingame overlay tool which gives valuable system information and reports when hardware works close to critical state
How To See Your Game's Frames Per Second (FPS) | Ubergizmo