Wikipedia
RivaTuner
RivaTuner is a freeware program developed by Alexey Nicolaychuk in 1997 for the NVIDIA video cards, from the Riva TNT to the GeForce 700 Series, which also has limited support for the ATI video cards from the Radeon 8500 and above.
It is one of the most common programs used for overclocking GPUs. It allows driver-level Direct3D and OpenGL tweaking (only in the NVIDIA video cards) and low-level hardware access.
It supports NVIDIA drivers from Detonator 2.08 to the newest ForceWare.
RivaTuner currently works with Windows 2000, Windows Server 2003 x32, Windows XP, Windows Vista, Windows 7, Windows 8, and Windows 10. It also works with the older Windows 98, 98 SE and Me, but they are no longer officially supported.