More than just fan control, the Nexus monitors temperatures, provides alarm warnings, and provides USB and FireWire connectivity.
"The LCD display displays the system information your interested in with the touch of a button. There are three temperature probes included with the Nexus, and all you have to do is attach them to whatever it is you want to monitor. I would imagine the most likely combination is the CPU, hard drive and system. However, you can choose to watch the video card, your memory or even your Northbridge. It's up to you. Another nice feature is the LCD is backlit, so even in the dark, you can still read the LCD."
Review Link : Viper's Lair