SpeedFan - Hardware monitor for Windows that can access digital temperature sensors located on several 2-wire SMBus Serial Bus. Can access voltages and fan speeds and control fan speeds. Includes technical articles and docs.
CoreCtrl - CoreCtrl is a Free and Open Source GNU/Linux application that allows you to control with ease your computer hardware using application profiles.
Open Hardware Monitor - Monitors temperature sensors, fan speeds, voltages, load and clock speeds, with optional graph.
NoteBook FanControl - This software detects and optionally controls speed of CPU fan of many PC-Systems.
iMac HDD Fan Control - iMac HDD Fan Control is an HDD fan control for the Mac operating systems by using which the Mac users can control the speed and noise of the fan of the Mac.
thinkfan - Thinkfan is a simple, lightweight fan control program.