GPUTool is described as 'Used to alter clock speed on NVIDIA graphics cards' and is an app in the System & Hardware category. There are more than 10 alternatives to GPUTool for a variety of platforms, including Windows, Linux, Android, iPhone and Mono. The best alternative is Open Hardware Monitor, which is both free and Open Source. Other great apps like GPUTool are MSI Afterburner (Free), RivaTuner (Free), CoreCtrl (Free, Open Source) and ASUS GPU Tweak III (Free).
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.