Coolbits was a Windows registry hack for Nvidia graphics cards Windows drivers, that allows tweaking features via the Nvidia driver control panel (including overclocking). There is also a Coolbits 2.0, with extra features. These features provided by Coolbits are considered expert-only and thus the reason they are normally hidden in the control panel.
Below is the main Coolbits activation entry in the registry:
[HKEY_LOCAL_MACHINE\SOFTWARE\NVIDIA Corporation\Global\NvTweak] "CoolBits"=dword:00000003
|NVIDIA Overclocking||Succeeded by
NVIDIA System Tools
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