NVClock is described as 'small utility that allows users to overclock NVIDIA based video cards running on the Linux platform. The original code used in building this application was borrowed from the nvcs application' and is an app in the System & Hardware category. There are eight alternatives to NVClock for Windows, Linux and Mac. The best alternative is ASUS GPU Tweak III, which is free. Other great apps like NVClock are EVGA PrecisionX 16 (Free), PowerStrip (Paid), ATI Tray Tools (Free) and GMABooster (Free).
ASUS GPU Tweak III is currently open beta testing so try it out, if you feel it is missing something crucial give ASUS your feedback & they may be able to add it while still in beta. So far ASUS has been very accommodating with all useful feedback.
This tool is developed by Ray Adams. ATI Tray Tools is a Full Featured Radeon Tweaker that can be found in the windows tray which then allows instant access to options and settings. Quite handy and quite a small download. Just click the executable and you are good to go.
NVTray provides some extra quality tweaks that both the default NVIDIA tray icon and control panel are lacking. I especially wanted to be able to select more Antialiasing modes, as well as OpenGL and Direct3D options right from the tray icon.