k10ctl is a P-State utility for AMD family 10h (aka K10) processors. It can modify the P-States, i.e. alter processor and the northbridge frequencies and voltages, set or change the P-State, and read out frequency and voltage information. The main purpose of k10ctl is overclocking or "undervolting" the CPU and to configure Cool'n'Quiet settings.
c2ctl is a frequency and voltage modification utility mainly intended for Intel Core 2 and Core CPUs. It should also work for other CPUs (namely processors with SpeedStep). The utility can also enable SpeedStep (e.g. if it was disabled by the BIOS due to overclocking) and read out frequency and voltage information. The main purpose of c2ctl is overclocking or "undervolting" and to enable SpeedStep.
katimon is an unofficial ATI graphics card temperature monitor, fan regulator, and overclocking utility. It is a graphical front-end to the command-line aticonfig utility. Katimon monitors and controls supported ATI graphics cards. It can monitor temperature, fan speed, GPU speed and memory speed. It can automatically control fan speed by monitoring the temperature. It can also act as an overclocking utility for cards that support it. This utility only works with the proprietary fglrx driver.